Old thread already, poster probably gone. However, is it possible to save the icon for the button that you want, then insert a pound sign into it using an art program such as Photoshop, or even Paint? Then that modified button would be loaded and it would already have the sign in it.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw