What is the circle with a line through it?

The circle with a line through it, also known as the prohibition sign or no symbol, is a common graphical symbol used to indicate something is not permitted or allowed. The symbol consists of a red circle with a diagonal line through the center from top left to bottom right. It’s a very simple yet effective way to communicate restriction or unavailability quickly and visually.

Common Uses

Some common uses of the prohibition sign or circle with a line through it include:

  • Indicating that something is not allowed, prohibited, or forbidden
  • Signifying that something is incorrect, not applicable, or invalid
  • Denoting that a specific action cannot or should not be taken
  • Marking that an item is out of stock or unavailable
  • Displaying that a utility or function is disabled or turned off
  • Signaling “no,” “do not,” “stop,” or “wrong way”
  • Symbolizing a restriction such as “no smoking,” “no cell phones,” or “no food or drink”

The circle slash is commonly used in signage and labeling in public spaces such as parks, schools, airports, and facilities to denote rules and restrictions. It appears on products to indicate incompatibility or lack of a feature. We also see it frequently in user interfaces and on controls to represent disabled, inactive, or blocked functions.


The origins of the prohibition sign can be traced back to the late 19th century. As automobiles became more popular in the early 1900s, road signs started utilizing the circle slash symbol to mark prohibited actions for drivers. One of the first known uses was on signage along the Alaska Highway during its construction in the 1940s to denote areas that were impassable or hazardous for cars.

The symbol grew in prominence after World War II and began to replace more text-heavy signage in public spaces. Its ability to convey a concise visual message transcending language barriers increased its use internationally. Today, the prohibition sign is standardized in the ISO 7010 standard for safety signs and is universally recognized.


The main meaning behind the circle with a line through it is to prohibit or forbid something. The circle indicates something is present while the diagonal line visually negates or cancels it out. Together, they form a clear symbolic message of restriction or unavailability. It’s like a red stop sign in a simple geometric form.

Placing the diagonal line at an angle through the circle makes it highly visible and distinct from the filled circle symbol which usually indicates mandatory actions. The boldness and asymmetry of the diagonal line are key to clearly conveying the prohibitive meaning. Subtle differences in orientation, slope, line weight, and color can alter the nuances of meaning.


The prohibition sign psychology operates on multiple levels. Its bold red color grabs attention and alerts us to the importance of the message. Red has innate biological significance, associating with danger, warnings, and important signals. The asymmetry and tilted orientation of the diagonal line increase arousal levels and vigilance per psychological principles such as the oblique effect.

The contrast of the diagonal line against the circle engages the brain’s innate preference for pattern recognition and disturbance of expected patterns. The filled circle represents completeness while the line violates that expectation of closure, making it more salient. The meaning is decoded almost instantly due to its pictorial nature rather than requiring literacy to interpret text.

Finally, the sign shapes behavior and actions by tapping into our unconscious rule-following impulses and avoidance of threats. It evokes conformity by implying rules that should not be broken. Placing it strategically in environments elicits compliance and self-regulation aligned with the intent of the sign.


Certain variations in the prohibition sign can change its meaning and implications:

  • Color – Red is standard but other colors like black, gray, or yellow are sometimes used
  • Circle size – Larger circles increase visibility and impact
  • Line angle – More vertical angles feel more restrictive than diagonal slashes
  • Line weight – Thicker lines increase the sense of authority and sternness
  • Crossing line – Two crossing diagonal lines indicate a stronger prohibition
  • borders – Borders around the circle further accentuate the sign
  • Text – Adding text like “No” clarifies meaning for avoidance of ambiguity
  • Symbols – Icons inside the circle denote what is prohibited, like no smoking or no cellphones

These variations allow the prohibition sign to be customized for specific contexts and meanings while retaining recognizability. A prohibitive meaning is conveyed across all variants.

Cultural Differences

While the general meaning of the prohibition sign is consistent, some cultural differences in interpretation and associations exist:

  • In Europe, crossed diagonal lines are more common than a single line to represent restriction
  • In China, a cross inside a circle indicates prohibition more so than a diagonal slash
  • In Japan, the circle slash is associated with meaning “wrong” in addition to “not allowed”
  • In some Muslim countries, the sign evokes religious connotations of forbidden haram behaviors
  • Colors like white and blue are preferred over red in some cultures
  • More permissive cultures may see the sign as only a suggestion rather than a strong rule

Understanding these nuances allows appropriate cultural adaptation of the circle slash symbol for clarity and alignment with local norms.

Design Principles

Some key design principles to ensure the prohibition sign is effective:

  • Place prominently at points of interaction to convey the message
  • Use high contrast colors like red/black or white/black for visibility
  • Make large enough to be visible from a distance
  • Use simple, bold shapes for fast recognition
  • Orient the diagonal line for visual flow towards points of interest
  • Add explanatory text or icons if needed for clarity
  • Standardize across contexts for consistency

Following basic visual hierarchy, visibility, and graphic design principles enables the sign to clearly and intuitively communicate the intended prohibitive meaning.

Common Confusions

Some commonly confused symbols with the prohibition sign include:

Symbol Meaning
Slash inside a circle Prohibition/Restriction
Filled circle Mandatory Action
Empty circle Optional Action
Circle with check mark Approval or correctness
Triangle with exclamation Warning

It’s important not to confuse the circle slash with other similar shapes and icons which have different meanings. Placement in context helps differentiate the prohibition sign from these other symbols.


The prohibition sign has many applications across various domains and contexts:

  • Signage – Widely used in public signage like no smoking, no parking, no cell phone use, etc.
  • Transportation – Used on roads for no U-turn, no left turn, no entry, etc.
  • Environment – Denotes protected or restricted areas in natural parks and wildlife zones.
  • Facilities – Indicates rules and restrictions in places like schools, offices, museums.
  • Technology – Signifies disabled functions or features in software, apps, websites.
  • Retail – Communicates unavailability of products, items not allowed in stores.
  • Events – Used to set rules at concerts, festivals, conventions, and venues.

The flexibility and broad recognition of the circle slash allow it to effectively indicate prohibitions across many contexts. Placement in the environment prompts compliance with intended regulations.


Key benefits of using the prohibition sign or circle with diagonal line include:

  • Universally recognized meaning of disallowance or restriction
  • Conveys clear visual message quickly at a glance
  • Draws attention with bold, contrasting shape
  • Simpler and faster to interpret than text
  • Reminds and reinforces rules and norms
  • Transcends verbal and cultural barriers
  • Memorable and effective prompt for compliance

The circle slash has stood the test of time as an iconic symbolic shorthand for prohibiting actions and denoting unavailability. Its simplicity across cultures along with its association with regulation make it a ubiquitous and indispensable graphical device.


Some representative examples of the prohibition sign or circle slash symbol in real world applications:

  • No smoking signs
  • No cell phone use signs in schools and hospitals
  • No food or drink signs in libraries, labs, clean rooms
  • Do not enter, do not pass road signs on highways
  • No parking allowed notices in restricted zones
  • Unavailable or sold-out items denoted online or in stores
  • Disabled, inactive, or inaccessible features in software interfaces
  • Age restrictions for entry to venues serving alcohol
  • Protected or fragile artifact signs in museums
  • Unsafe areas marked in wildlife parks and hiking trails

These samples demonstrate the wide range of applicability for the circle slash prohibition symbol across public, private, digital, and environmental contexts.


The prohibition sign of a circle with a diagonal line is an iconic, shorthand symbol that conveys a message of restriction, unavailability, or invalidity. Derived from late 19th century signage, it became popularized internationally in the 20th century through transportation systems, public spaces, and eventually digital UIs. The high contrast and asymmetric shape psychologically grab attention while tapping into rule-following mentalities.

Universally understood due to its pictorial simplicity, the circle slash effectively regulates behavior and perceptions. It will likely continue serving critical symbolic functions as new contexts emerge. The next time you come across the prohibition sign, pause to admire its concise graphical ingenuity.