Just came across this: http://youtu.be/rit7WdMRxQo
Flat track roller derby referee hand signals for beginners
With a snowy Helsinki as the backdrop, referees from Helsinki Roller Derby demonstrate all of the Women's Flat Track Derby Association's referee hand signals, accompanied by the official verbal cues. The hand signals reflect the update released December 7, 2010, and the verbal cues the update issued on December 30 2010. We are not affiliated with the WFTDA nor do we represent them. (but we do hope to be members some day
(NB They are a WFTDA Apprentice league now
It includes signals that are not official but commonly used and some that don't appear on the rules appendix.