This is an example of legislation that may have started with good intentions, but after going through numerous subcommittees and committees and consideration/scrutiny by people who are not fluent in plain english (their first language being bureaucratese) and placed on the ballot and passed by California voters who never read the text of the proposition.
Apparently it is required to either have labeling on retail packaging or signage at the entrance of buildings if there are any chemicals that may cause cancer in the item or in the building. Apparently there is no requirement to divulge the actual chemical substance that may cause cancer nor is there a requirement to provide the scientific studies linking those substances and carcinogenicity (some of the studies may have exposed the animals to unrealistically high levels).
I am not too sure what the real benefit of Prop 65 if all it does is basically say--danger, be careful, but does nothing to let the consumer know what the danger is.
Many items that we use have the Prop 65 notices in them.