If the only issue you have is that is that Shift-3 should be # then a solution is to change the input source to Australian rather than British.
This is a duplicate of my answer on Stack Overflow
I assume that you have a Mac UK keyboard so Shift-3 is £. On most other keyboards Shift-3 is # as others have said.
The way I get round it is to change the input source to Australian the only difference is that Shift-3 is now # and Alt-3 is £ (or leave as the emacs binding)
Input Source setting
was System Preferences->Language&text->Input Source
On later OSX versions (OSX 10.11 definitely but would have been earlier) Input Source setting is System Preferences->Keyboard->Input Source By default this will just show the UK keyboard to see more hit the + at the bottom of the list and add Australian
There are conflicting reports on similar answers that choosing an Irish input source might or might not work.