Limitations on Mexican Flights

Why do they use $ for both currencies, just asking for trouble.

They both stole the $ sign from Mexico.

Rob is correct. However, the origins of how and why and when are all very murky. Some say that the original U.S. dollar sign was a superimposition of U and S. Some say that the U.S. dollar sign was written with two vertical lines to differentiate it from the peso. There are various other theories.

Wikipedia's Take on the Origins of the United States Dollar Sign