It is often said that we should not pick up spare coins lying on the road. In Eastern India the Tantra style is very popular and it is often speculated that people leave them intentionally on the road after casting a spell on it.
Money is Lakshmi, she is the Goddess of Venus and to ignore her would be heinous crime. If really there is no rightful owner found you should pick it up and give it to some beggar.
I read people are suggesting that you put it in temple donation box that you may do as well. I suspect that is where the coin was lying earlier until God decided to put it in your path to test you. I am not sure why God needs money. I would rather give it away to beggars.
Nothing is bad in getting coin from anywhere excluding shmashana (graveyard). Going to temple is also a good thing but if in your horoscope four houses 6- 8–12 all are with planets and if 2nd house is empty and most of planets are enemy than don’t touch any statue just pray from outside.
However, some believe that there is nothing good or bad in getting (accidental find) a coin which belongs to somebody. It might not be better to keep the coin, instead it should be given away (as alms) to poor and needy as we do not know who lost it and how much they might have needed it!
