You mean #? Or something different? If it is # then it's Alt-3 on a UK keyboard. Otherwise you can turn on the Character/Keyboard viewer in the menu bar that gives you access to pretty much every symbol.
ok but what about the other characters? I like to use ♫ ♪ and ♥ ¢ very offten, i dont want to be opening something on my menu bar everyt9ime and searching for these characters