What would I be asking you if I said heads or tails?
Would it help if I told you I had a coin in my hand?
Yes, I'd be asking you to make a choice in predicting which way up a coin would land when I tossed it.
This method of decision making is still used at the beginning of many sporting events. The head side has the monarchs picture on; the other side may have a coat of arms, a gate or lion.
Here's a nice little film giving a short history of coins.