For a similar contraption in action, see Buster Keaton's 1922 film "Cops."

Those of us who ride our bicycles everywhere still use those hand signals.

If I recall correctly, they used to bend their left arm at the elbow, with the forearm pointing to the sky to signal a right turn. Not sure how they'd do that with this inflexible wooden arm.

[It's hinged at the wrist. - Dave]

Is it possible there's another wooden arm on the passenger side?

[It's a substitute for a regular hand signal. Which you'd give on the driver side using your arm to indicate either left or right turns, as well as stops. You wouldn't need one on the other side. - Dave]

I watched a video on the Jay Leno's Garage website the other night, about his Tatra T87 car, built before WW2.

It had the same sort of turn signal, only it was a little wand that flipped out. Jay said it was a handy thing for when you were out for a drive and stopped at an intersection. You could call a pedestrian over to visit and whap them in the head as they bent over to the window.

Maybe you just pull the rope part way for a left turn and pull a little more for a right. Looks like it could go higher than horizontal.

From the Ford Motor Co. credit in the caption I guess this was taken for promotional purposes, showing the Model T hard at work. However, if that is the case, unlike most promotional material I've seen, this shows a very used and slightly battered example. I love the scrollwork brackets by the driver's head.

"We Wash Everything but the Baby"

Located at Blair Road and Butternut Street NW in the Takoma Park section of Washington. The president and manager was Gordon W. Bonnette, perhaps that's him in the doorway.

Check out the state of the art turn signal (wooden hand just outside drivers door). Just pull the rope inside for a left turn. Umm, what do you do for a right? Maybe they only made lefts.