Is it an OSHA mandate to post first aid signage over the first aid cabinet?

While highly recommended, 29 CFR 1910.151 does not specifically require a first aid kit location sign.

However, 1910.151 Appendix A states that “First aid supplies are required to be readily available under paragraph 1910.151(b). An example of the minimal contents of a generic first aid kit is described in American National Standard (ANSI) Z308.1-1998 ‘Minimum Requirements for Workplace First-aid Kits.’” ANSI Z308.1-1998 calls for unit packages to be labeled and color coded; however, the standard does not recommend a sign. On the other hand, note that ANSI Z308.1-2015 does recommend “Each kit and/or location shall be visibly marked as a place where first aid supplies are located.” Also note that ANSI just approved the 2021 edition of ANSI Z308.1, but it does not yet appear to be released for publication, and we do not have a copy. It “likely” has a location sign recommendation, however.

OSHA does not specifically require certain colors for “first-aid” signs. However, according to 1910.145(a)(1), if an employer determines that the nature of the hazard is such that failure to designate it may lead to an accidental injury, then a sign, in accordance with 1910.145, or other effective means (like proper training) is required. Otherwise, a sign is optional.