That is a good question. I go to a local hot spring and there is an elderly gentleman that always has part of his junk hanging below the hem of his swim shorts. It seems like that is something a guy would notice but he does not seem like a freak in other ways
My zippers have a mind of their own. However for a woman wanting to strike up a conversation with a man, it's a good pick-up line. But if a man should tell me, I'd probably wonder why he noticed. Personally I have never looked at a man's zipper. Nada, not once.