According to the ISO standard (and also under a UK Statutory Instrument), the red area must take up at least 35 percent of the total area of the sign within the outer circumference of the … 展开

Motor vehicle traffic signage
The "prohibition" symbol is used on traffic signs, so that drivers can interpret traffic laws quickly while driving. For example:
• No left turn or No … 展开

Non-conforming designs
Despite the fact that the ISO standard is freely available, it is not uncommon for graphic artists to improvise on the particular color and … 展开

• Federal Highway Administration
• ISO 3864
• List of international common standards 展开

The official prohibition sign design characteristics are governed by regional and international standards. The symbol's canonical definition comes from the International Organization for Standardization which published ISO 3864-1 in … 展开

Unicode combining character
The Unicode code point for the prohibition sign is U+20E0 ⃠ COMBINING ENCLOSING CIRCLE BACKSLASH. It is a combining character, which means that it appears on top of the character immediately before it. 展开

• UK legislation regarding health and safety signs, The Health and Safety (Safety Signs and Signals) Regulations 1996 (SI 341)
• UK legislation regarding road signs
• Working drafts for UK road signage 展开