[Milsurplus] marking on R-388/URR

[Joe LeKostaj]

Hi.  I'm a rank beginner when it comes to mil gear, so maybe this is 
an elementary question. I've got a R-388/URR that has a square red 
ink stamp in the upper right corner of the front panel. Can anybody 
tell me what this mark means? It is about one inch square, with a 
large letter "A" in the middle and smaller letters "s" and "c" to the 
left and right respectively. Below the crossbar of the "A" is the 
number 1305.  Could this possibly refer to Strategic Air Command? I 
hope someone can shed some light on this.

Tnx & 73,
Joe K9LY