Background: I am creating a graphical game which will be deployed on both mobile and desktop platforms, and across many cultures/languages. When the user sees a screen where there's an opportunity for in app purchase, I want to darken the whole screen and overlay with a "Purchase" button. I won't show the price here, hitting the button will navigate to a different screen where they can make the purchase. So I want to just display the word "Purchase" or "Buy" and a graphical symbol, since I suspect that text by itself will be boring.
The ideas I've toyed with are:
Idea 1: "$", "$$", etc. -- This is more work to localize, and there may be some cultures where a currency sign or abbreviation by itself could just cause confusion.
Idea 2: Symbolic picture of bills and coins. These would be cartooney enough that you couldn't actually make out what country they were from, but I think they could still be recognizable. I'm thinking silver and/or gold coins and green bills if color is used. Psychologically speaking, I'm not sure that I want to emphasize the user parting with "pile of money", though. :)
Idea 3: Shopping cart silhouette -- This seems to be widely used and is my default answer so far, but I think there has to be something better.
Is there a standard answer here or one better than mine? Thanks for reading.