I can't stop thinking of this

Actually, from what I understand, these messages were put there because a lot of parents - not necessarily incorrectly - associated arcades with a seedy element. Arcades were known as a place where some 'stuff' might go down. By putting a message like this onto their games, arcade manufacturers hoped that they could help reassure parents that they weren't trying to support the drug culture, and therefore their kids would be okay to come spend quarters on the games - now it was a "positive" environment.

I'm sure that for some concerned conservative parents (and I don't mean that in a political way, and I don't think you did either) it helped them feel like their kids could go drop quarters in the new pinball machine and it would encourage them to make good choices in life, thus making the arcade companies more money in the long run.