What's the point of the "proper" hand signal system when most people don't know it??? Either way, the right arm outstretched is a clear signal that only willfully ignorant drivers won't understand. Even though I'm on a fixed gear bike with only a right-hand brake, I stretch out my right hand for right turns and lane changes. People know what you're doing.

And wait -- besides, it's not important to just lift up your arm. If you want drivers to take you seriously you gotta really stick it out there. You're flagging the drivers. A left hand turned upwards is weak and I don't think it's a very safe signal.