The following warning label must appear on products sold in California if they contain chemicals on the Proposition 65 list of hazardous substances.

WARNING: This product contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm.

The wording can be changed as necessary, so long as it communicates that the chemical in question is known to the state to cause cancer, or birth defects or other reproductive harm. Common variations include "This area contains chemicals known to the State of California to cause cancer, or birth defects or other reproductive harm" or "Chemicals known to the State of California to cause cancer, or birth defects or other reproductive harm may be present in food or beverages sold or served here."[4]

Some businesses in the state post similar notices on their premises, even when they are unaware of any listed chemicals being present.[5] Warning signs are often posted at gas stations,[6] hardware suppliers,[7] grocery stores, drug stores, medical facilities, and many other businesses.[8][9] Government agencies,[10] parking garages, hotels,[9] apartment complexes,[11] retail stores,[12] banks, and restaurants[13] also post warning signs because of the possibility of hazardous chemicals being present in everyday items or the nearby environment. Some large businesses, such as utility companies, mail a Prop 65 notice to all customers each year to warn them of dangerous substances like natural gas[14] or the sand used in sandblasting.[15][dead link]

There is no penalty for posting an unnecessary warning sign.[16] Because of the overuse of the vague warning, the ubiquitous signs ultimately communicate very little information to the end user.[6][17] This problem has been recognized by California courts,[18][19] advocates,[6][20] and businesses.[9]