Drugs are disallowed on these premises. No Alcohol or Illegal Drugs Allowed at This Workplace is posted as a prohibition sign. declares that actions or activities that are prohibited shall be marked with Prohibition Signs. Commonly, prohibitive signs are used to designate activities that are either prohibited because they violate the laws and ordinances of a particular location or because they may endanger the health and safety of onlookers. A prohibition sign is a placard that forbids actions that could escalate or pose a risk (such as smoking). Round form is an intrinsic property. Indicating that a particular act is forbidden, prohibition signs are likewise red. Red restriction signs typically display the restricted item as a black emblem with a red crossed circle on a white backdrop.