To sign money, hold your non-dominant hand out as if begging for alms. Then take your dominant hand with your thumb touching your fingers, forming a bent 'O' hand, and tap it against the fingers of your weak hand. It is like you are demanding to be paid now!
Anything that adults touch, babies want to touch. So of course, money fascinates children. Make it into a game, and when your baby makes the money sign, give them some play money. Then you make the money sign back, and they give it back to you. Congratulations, you have just been indoctrinated into our socialist agenda!
There is no way around it; eventually, your baby will become familiar with currency. Teach the concept at the store when handling cash transactions, or at home when encouraging habits such as saving or helping out.
Get all four volumes of Baby Signing Time...