I don't think "flipping the bird" is specific, it's either "I'm a jerk" or "I'm angry [with you]" but they both seem pretty wide ranging.

Pointing is really none specific, do you want it, want to look at it, want someone else to hold it, etc..

Military and crane operator signs seem like they're limited sign languages. Excellent example.

Driving is a good one, but it's 3 specific signs, and then pointing. I'm often annoyed that other drivers don't know BSL!

Thanks for illustrating the point, very helpful.