Well, I was lucky I found it. And if I pass it on to a charity collection box (what I usually do), then they are lucky to have got another contribution, and the end recipient probably needs it more than I do. If I am willing to share, instead of keeping it all for myself, then I find life has a way of returning the favour. Win Win all round.
Lucky penny? Of course. Some people call them Angel Kisses.
I think the penny becomes lucky because you pass it on - whether you find it yourself or if you start the cycle by giving one of your own - or indeed if you buy one, but pass it on to someone who may need it more. Hugging it to yourself suggests a little ... greed ... wanting it all just for you ... unless you really are in dire straits
Oh, by the way, over here in Ireland the rhyme goes "see a pin and pick it up...." I'm not at all sure about the luck element there, except that perhaps you were lucky to find it.