You mean visually or when they are near you? Visually I understand because both are yellow so is not so clear from one and other, and I'm sorry for that. If it's the latter when your character is green and a number on top there's a coin near you, when it turns yellow there's a bomb near you, it doesn't matter if there's a coin as well, so the best option is to move around to see if you can turn green again. I hope that I solve your question either way, thanks for playing the game!!! :3