Create a Global Shortcut for a Single Letter
One relatively simple method is to assign a text input that is then converted into "w" when you type your sequence.

I have chosen to type "(v)" that is converted to "w", but you can choose what suits you best (and what you can remember).

Open Keyboard-Text pref in the System Preferences, as described in this Apple Support page.

Click on the + sign to add a new item.

Now first type your choice, then paste a "w" in the right column.



It will work on almost all OS X apps, but won't work on web pages like this one.