I didn't mean for the definition to be taken literally.  I'm just saying the concept of "approximately equal to" already associated with the tilde would make for an easy transition into thinking of the tilde as a currency symbol.  The tilde means "approximately equal" when it is between two entities like this: a~b.  I think it could take on its own meaning as a currency symbol if it just trails a number like this: 20.99~.