The weather is warming up, and more and more motorcyclists are riding around. It’s hard, if not impossible, to communicate to other people at travel speeds. We have to rely on hand signals, and here are some of the more common ones.
Left turn
Arm pointing straight out to the side:
Right turn
Arm bent at a 90° angle:
Stop
Same as right turn, but pointing down …. We shot this picture but for some reason it didn’t make the transfer from the camera to the computer.
Speed up
Arm straight out, palm up, motioning upwards:
Slow down
Arm straight out, palm down, motioning downwards:
Hi!
Say hello to other motorcyclists. Arm straight out and down low. Some folks throw a peace sign, devil horns, or wave, I usually do “V for victory.”
Cop ahead
Close your hand into a fist and bonk the top of your head. I’ve also seen people pat the top of their head. Repeat frantically until the oncoming motorist responds.
Lane incursion response
Typically displayed after using your horn to ward of an incoming Ford Expedition piloted by a soccer mom beating her children while eating a Frosty from Wendy’s:
Did I miss any? Besides the obvious one-finger salute? 
I’ve always depended on my turn signals and brake lights. If I’m disappearing in front of you, you might want to speed up. If you are riding up my rear, you might want to slow down. I never worry about telling people they are being stupid, either they already know it, or they are to stupid to understand why you are upset.
Always plan for people to do the most dangerous thing possible, they way you are always pleasantly surprised.
I was just about to mention the one finger salute but you beat me to it. I find the one with the police coming really funny, way to catch someone’s attention.
Hi Brice,
Like you, I rely on my turn signals and brake lights most of the time. I never use hand signals for communicating intent with automobiles (unless they are following our riding group, like friends or whatever).
I use hand signals a lot when leading a riding group of four or more bikes. It’s sometimes hard for riders in the back to see turn signals if we’re staggered.
I did forget one hand signal I use exclusively (so far) with cagers: a “hang up” phone motion with my left hand. This is commonly deployed when someone on the phone slides into my lane.
I occasionally use this one when I encounter someone talking/texting/eating/reading. It seems to work a bit better than your “two palms up/shoulder shrug” that I used to do.
Point towards my eyes, then turn it towards the road ahead… they usually get the idea.
http://www.policeone.com/policeone/data/art-signs-watch.jpg
Another one that we use around here comes into play when riding with others.. its the “you’ve left your turn signal on AGAIN” signal.
arm out and down like the STOP signal, but opening and closing the hand, fingers spread wide.
http://njmc.org/etiquette/
There are a few more I use that you’re missing.
Arm like a right turn, but with a fist, and moving up and down. Like the motion to get a trucker to honk his horn–means “tighten up”. Used when bikes in a group get too spread out and it’s making moving as one vehicle difficult.
Arm raised with index finger in the air–means “single file”. Typically used in twisties where apexing becomes important. Rather than trying to ride in staggered formation, bikes spread out and go single-file.
Arm raised with index finger and pinkie in the air, like throwing up the horns–means “staggered formation”. Gets a group of bikes back in formation after a time of riding single-file.