Do you mean like having something at the bottom of the screen which displays the number of credits/coins inserted only when the front-end is on - or even when you are in a game? Not quite understanding your idea. Also I dont think there isn't a way for the front-end to tell the game how many credits have been inserted if that's what you had in mind
eg when in the front end you put in 2 coins, the bottom of the screen says CREDITS:2, when you select a game you'll still have to add credits in the game.
I do agree that it would look more arcade-ish having "CREDITS:2" somewhere on the screen, but maybe you could just incorporate it as an image instead of having to code something. Unless of course you want to make sure people enter credits before they can get into a game - that would be another reason.