What's this button do? '57 Roadmonster

[The other 455]

On the far left of my dash, there is a round knob. Just to the left of the speedo warning adjust (marked accessory!)
It pulls out in two step's like an old headlight switch, but it does not turn.
Nothing seems to happen, & my ebay purchased owners manual hasn't arrived yet.
Anyone know what it does?

[Nailhead58]

Is this button plain chrome, or does it have a red lens in the center? I had a '58 Limited, which has essentially the same dash, and it had a knob where your appears to be, that pulled out. It had a red lens that lit up when the knob was pulled, and it activated four-way flashers. The knob was a near match to the other knobs on the dash, so I believe it may have been a dealer-installed option. I think I'd look for wires, and see if there's a flasher in the circuit somewhere.

[Leviathan]

AH! That's why my bathroom light keeps going off and on!