Caution Low Head Room Sign, Philadelphia Transit Concourse in album signs

In Albums: Philadelphia transit signs

A sign on a low ceiling reading: caution, low head room, showing a picture of a person's head and a bump, with the person saying ouch

Jul 5th, 2011, by Alex Zorach

I find this sign in the Philadelphia transit concourse highly amusing. This sign is located in one of the areas that crosses over the Market-Frankford line tracks, and under Market street.