[Milsurplus] signal corps stamp

[Bruce MacMillan]

Last night a friend gave me an RCA AVR-11 receiver. From the little info 
on the web it appears to be an airport receiver. The one I have though 
comes from a marine enviroment. It has an extra switch added to the 
speaker panel marked CABIN - DECK.
On the back of the speaker panel is a black acceptance stamp about 3/4" 
square marked "SC 91 A".  Could this be Signal Corps stamp?

Bruce   ve7mt