Just be aware that the ONLY legal product marking on products sold in or exported to Europe for EU RoHS compliance is the CE mark. Strictly any other marking, eg green check marks etc,  are illegal

I'm not an expert on Prop 65 but the law text states 

"The manufacturer, producer, packager, importer, supplier, or distributor of a product may comply with this article either by providing a warning on the product label or labeling that satisfies Section 25249.6 of the Act, or by providing a written notice directly to the authorized agent for a retail seller who is subject to Section 25249.6 of the Act"

and that...

“Label” means a display of written, printed or graphic material that is printed on or affixed to a product or its immediate container or wrapper.

“Labeling” means any written, printed, graphic, or electronically provided communication that accompanies a product, such as a package insert.

Seems like a suitable explanatory paper note packed with the product would suffice if you feel that your product is likely to cause exposure to consumers to any listed chemicals at levels which pose a significant risk of cancer or observed to cause birth defects or other reproductive harm