DOCBOOK: character entities for keycap symbols?

Is there a set of character entities that represent keycap symbols commonly used in computer books? In this instance, I'm specifically looking for the Control
Key Symbol of Apple MAC Keyboard. 

If such a set does not already exist, the DocBook activity might be the best place to come up with a comprehensive list of character entities to represent commonly used keycap symbols.

Sunthar Visuvalingam
Research and Development
InformIT (Pearson Education)
www.informIT.com