"How do you know if a guy is showing interest?"

In my perception, most of the time you won't, because for a lot of guys, the fear of being rejected is too severe. I think a lot of men worry their interests will be perceived as "creepy" or "inappropriate" or as harassment.

So to me it seems like a lot of men will drop very subtle hints that may often go entirely unnoticed, or in this possible case, do seemingly random things in the hopes that the woman will connect the dots.

I think that in most cases, it's necessary to give clear signs that you're interested in the guy, to give him the confidence to be more direct.