I see that hand signals continue to be a topic of interest on some biking blogs. We all know the basic signals (As in the diagrams on the linked page, I signal a right turn by pointing my right arm straight out — I think there’s less chance of confusion).
But this discussion got me wondering about a motion I see on some group rides. Cyclists will put their (usually) left hand down when signaling slow or stop, and waggle the hand if they’re pointing out road debris.

But sometimes, they’ll move the left hand to the small of their back. And sometimes, they’ll hold it there stationary but other times, they’ll move it back and forth, as though they’re pointing to the right with their left hand — behind their back. To make matters more confusing, sometimes they’ll do the same signal with their right hand.
I’ve read that this can be considered an alternate sign for stop, but I don’t think so. I think it’s to indicate that bikers should move over to avoid an upcoming obstacle — for example, if a car is parked in a bike lane and we have to move left into the traffic lane to get around it, the signal would be made with the right hand.
But I’m just guessing. I haven’t come across any explanation of this signal in biking books or online. Because it’s a non-standard signal, it can cause confusion. And confusion can cause problems. What do you think? Is this a hand signal worth keeping around and promoting, or is it one best done away with?
around these parts, I’ve never known it to mean anything other than ‘stopping’ or perhaps ‘approaching a stop’. I suppose it could more precisely be construed as “I’m not going to blow through this stop sign that you can already see up ahead.” The primary variation is to have it be an open palm, and I suppose the shake is for emphasis.
On a side note, the old holding-your-left-arm at a 90 degree angle to signal turning right is stupid. As if your right hand is totally necessary for operating the bike. In fact, I almost never ever signal while riding alone. I indicate my direction of travel with the sheer force of my presence. If I want to take a left, drivers will know it because I will be on the left edge of the lane and also not moving. Signaling right is pretty much unnecessary.
Funny you mention this sign. Just saw it used on my first group ride in Houston. At least one rider used it to signal that he was finished with his pull and was ready to drop back. I had never seen it before, and in every paceline I’ve ever ridden in, the same sentiment was communicated with a subtle “chicken wing” of the elbow and/or simply moving slowly to the side and dropping 2-3 mph of speed. I don’t know if a closed fist on the back is the typically accepted signal for completing your pull, but that’s what they were using…
My left arm tends to go “numb” after riding for awhile. That’s the motion and position I use to get some “feeling” back.
I’ve seen it on most of the ACA group rides I’ve ever been on and it always referring to stopping.
Well I think I’ve seen that signal before, but I never did figure out what it was supposed to mean. I’ve only seen it in the context of group rides, so I’m assuming that it’s meant to communicate things to other riders. In that sense, maybe it’s OK if it’s not highly visible since the people it’s intended for are nearby. However, a signal no one understands isn’t worth much …
I have to agree with Bob. It is more than likely someone stretching their arm.
Around here it is used to communicate: slowing down to STOP!
“My back is killing me!”
I agree with Bob. While out touring this summer, I would often make this “signal” to stretch out a sore or numb arm after a long day of pedaling.
Itchy back?
This looks a lot to me like “fall in behind me” although I have never seen it don with a fist. Normally this is done pointing behind or to their tire, implying, “get in behind me, obstacle ahead”.
If it is dangerous to be off to the on-side (oncoming traffic in next lane), it is often accompanied with a waving motion to attract attention, with the size and speed on the wave indicating the size of the obstacle. e.g: single gentle wave ending in point behind: oncoming pedestrian; continuous fast waving: oncoming large pack moving fast – get in _now_ to avoid collision.