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What is the formal name for a circle with a line through it (often red in color) indicating that something behind the line is "off-limits"?

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For example, this sign indicating that one should not touch:

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  • ‘Forbidden’ sign is probably the most common, though I’m sure it has a more formal name also. Aug 15, 2019 at 13:57
  • Right. I searched for "off limits" and "forbidden" sign, but I didn't find any results that seemed like they provided a formal name. This symbol has lot's of names, so I wonder if one has been formally given.. Aug 15, 2019 at 13:59
  • That "don't touch" sign isn't very clear. At first glance I thought it meant "don't pick things up". Is the direction of the line standardised? The Ghostbusters sign has the line the other way.
    – nnnnnn
    Aug 15, 2019 at 14:27

2 Answers 2

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The general prohibition sign (official name, according to ISO 7010), also known as a no symbol, no sign, circle-backslash symbol, nay, interdictory circle or universal no, is a red circle with a red diagonal line through it (running from top left to bottom right), completely enclosing a pictogram to indicate something is not permitted. The symbol is sometimes black instead of red when color is not available.

ISO 7010 is an extension of ISO 3864-1 set in 2002.

ISO 3864-1 sets the rules for the color and shape of safety signage, as well as regulating the incorporation of text according to viewing distance and sign size. The range of color and shape defined in this standard for the "prohibition symbol" or "no symbol" is defined as "a prohibition surround shape (a red circular band with a red slash going from the upper left to the lower right) over the top of a black graphical symbol."

Source: Wikipedia

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    That reminds me of a handy reminder for UK roadsigns: the round ones are "nO", and the triangles (like an A) are for "bewAre". Don't ask my why "STOP" is ocatgonal though :) Aug 15, 2019 at 15:28
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According to ISO 7010, it's called a Prohibition sign (and a General prohibition sign if nothing is shown behind it). Wikipedia lists a few other common names in the article 'No symbol'.

The corresponding emoji, 🚫, is called the No Entry Sign, even though it

does not look like the no-entry road sign that one might expect.

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    Ah, I didn't even think to check ISO. Good find +1. However, I wonder if this symbol existed prior to ISO standards, and if so, I wonder if there is an older former naming convention that had been formally codified somewhere... Aug 15, 2019 at 14:04

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