I used the open / closed hand to tell a biker he had his indicator on - he waved back to me ! HAHA guess its not quite universal yet, or it may be the application from me…either way it was quite funny
Pointing at the tank - I need to stop for petrol.
Pointing at the exit we will take at the roundabout - take that exit :doze:
Arm out, thumb up - it’s safe to overtake (if you trust thumb person!).
Waving frantically - I have a KTM, please stop and help me fix it.
Tailgaters usually get a turn around staring evil if possible.
surely this should be the london bikers signal!
tailgating signal = start tyre scrubbing and watch them drop back 
as for pressing brakes … nope as all it does is cause severe domino effect and possible numpty when passing cutting you up and doing the same in return …
as all above similar signals and dont forget ( ok for the ktm owner)
helmet by rear wheel = Its bollocked please stop and help me
left foot wave if hands are busy
Im with Kato on the ‘leg out’ to thank bikers/ cages for letting me through… takes but a fraction of the thought and effort of waving, especially usefull when filtering!
The low hand with the open/close/open close for indicators is another classic as Kevsta said.
Probably me being pedantic, but personally i HATE the flashing hazzards for thanks…
Becareful when using this at a female biker, she can get the wrong meaning! 