Shingle
A shingle was a type of sign advertising the services of a professional, such as a doctor. 

In 2267, Doctor Leonard McCoy joked that he could throw away his shingle (i.e. quit his job) if the rest of the Omicron Ceti III inhabitants were as healthy as the nine he had already examined. Later, James T. Kirk noted McCoy's comments to Elias Sandoval. ()
Signage
Slang