I volunteer at the Saratoga Auto Museum . This 1922 Henderson is an unrestored Police bike, straight 4, suicide shift. It's a BIG piece of gear! Right behind the speedometer is a little stop light, it has power and an on-off switch at the rear of its base. The entire bike is blackish yet this item is nickel or polished something. My Dad was a glass blower, so I can tell you the glass is not a film over clear glass but glass with color all the way through.
What is its purpose? This can't be a 100 year old strobe of what we see on cop bike now is it?
It wouldn't be very visible to cars. That looks like it's behind the glove box on the tank, right?
Are there other beacons on the fenders? Its possible that's how you turn them on, and that little stoplight was just the indicator so the driver knew they were on. I mean, this was 1922 with low-output 6v lights. The police beacon lights were probably no brighter than turn signals. They could probably be flashing and the driver wouldn't know it unless the indicator was on.
Behind the ticket box, no other lights. Pretty cool indicator light. =~ )
More pics of the bike please.
ShawnG
UltimaDork
4/21/21 3:36 p.m.
Just an old indicator, I've seen them before. They're just for fun.
What does that what looks like an on/off switch or an adjustable something do.
ShawnG said:
Just an old indicator, I've seen them before. They're just for fun.
OMGWTFBBQ!?!? People put goofy things that pleased them on their cars/bikes back then? Somethings never change. 
Exterminate! Exterminate!
In reply to 914Driver :
I think it's just a running light to indicate that it was a police bike.
Is that a wire coming out of the bottom or is it an acetylene line? The knob is probably a switch or a flint striker.
My bet is that it's a gas light.
Is there an acetylene tank with a hand pump on it?
Is the headlight gas or electric?
a prewar police motorcycle with a gas-fired disco light is probably the coolest thing I'll see this week
ShawnG
UltimaDork
4/21/21 8:16 p.m.
It's just a light socket with a bulb. The jeweled thingy is a bulb cover.
You can still buy the same socket assembly. The lever sticking out of the side is the on/off switch. All it really does is rotate the contacts in the base of the socket into position to light the bulb.
Brillman has them, just pop the chrome hood off and install your disco cover: https://brillman.com/product/12-volt-chrome-finish-dash-lamp/
It's electric, there's a wire, also the headlight. There is a hole/opening on the front of the thing, almost big enough to put a finger into. Could be a spot for a bulb but I didn't see any fittings.
Hmm, very interesting. you said there is a hole in the light on the front. It also doesn't look like there is an integrated light in the speedo - that would be really novel tech on a bike that old if there was. So here's my guess - it's a light so the officer can see the speedometer, and it doubles as an early version of a police light showing people that you are the law.
Is this the same little light on an Indian?
Found some other interesting information.
that speedometer is called a "tattle tale speedometer" apparently. The second needle has a little post on it that would catch the actual driven needle, so it would get pushed up to whatever the rider's maximum speed was. Apparently intended to pace speeders and record the speed.
Corbin Screw Company made them, and I found a little oddball info in an ad here. Looks like 100 mph + speed record needle was optional: https://www.worthpoint.com/worthopedia/1927-corbin-car-truck-motorcycle-speedometer-catalog
Reproduction Corbin speedometer light, note similar knob:
I did find one other example of it, listed as "speedometer lamp":
Found one more, now I gotta stop and get some work done. I love obscure stuff like this.
this Henderson sold at Mecum had one on it as well:
https://www.mecum.com/lots/LV0117-262789/1931-henderson-four/
the Harley Davidson accessory guide back in the day lists a speedo and light, but it is not the version with reflectors/colored lenses on it.
https://www.ratbikeservice.com/HD/dwnld/Parts-Catalogs/1929%20Inspected%20%26%20Approved%20Accessories.pdf
I'm pretty sure I had one of these once, but I don't think I ever knew what it was.
Thanks Gearhead! That makes too much sense. Reply to Kendall-Jones: these are the only other pics I took yesterday.
In reply to 1988RedT2 :
Yeah, didn't read the that part well. My bad
