yep glue, if you want to know for sure get you some acetone from any major dept store. Not fingernail polish remover but pure acetone. It comes in handy
First, welcome to the neighborhood! Coins are often glued together because some people have nothing better to do. When the coins are separated, some of the glue will adhere to one coin or the other. Using 100% pure acetone will usually remove the glue without damaging the coin. Chris