in the "Signatures - Sign / Verify a Message" Window we have the keyboard shortcut alt+S and alt+V to switch tabs and the same shortcuts to Sign or Verify the message (These two buttons should be changed to alt+m and the shortcuts for the tabs should the same).
Tested with English and Swedish translations and client version 0.7.0 on 64-bit windows 7 and 0.7.1rc (compiled latest sources from github) on 64-bit ubuntu 12.4.