When first talking to a girl is there any type of clue as to whether she has a boyfriend and is there any question to coax it out of her?

Usually girls will talk about their bfs, but if not ask something like "will your boyfriend mind if i buy you a drink/cup of coffee.."

also look for a piece of jewelry she wears everday, usually that means that it has special meaning to it so maybe it was from a bf, compliment it and then ask about it.