Oh my lord, there'll be 17 pages of this before long...
I do find the Car Up and Car Down confusing because different groups, even around London, use it in different ways.
Consequently I find the easiest one to be Car Front and Car Back. It is impossible to misunderstand, and the words sound different enough to be made out even when not enunciated clearly. Dulwich Paragon certainly use this as a standard methodology.
To the OP - a variation of the arm bent diagonally behind the back is to stretch the arm behind and use a sweeping movement e.g. a pack move to the left (most common in Abu Dhabi) would involve the right arm outstretched behind the back and motioning towards the left.
Other signals I have encountered, not mentioned above:
Move to Single File: Forefinger extended (to indicate One) arm raised above the head and moving backwards and forwards in a line.
Speed Bumps: upper arm (either) out to the side at 90 degrees, lower arm and finger pointing down and moving to and fro to indicate the strip across the road.