GREEN TENO SIDECAP - w GREEN "TENO" UNIFORM - REVERSE SIDE of PHOTO
Here is the Back Side of the Same TENO Photo.
My German is not Great, but I think that it Reads:
"TN Man
GUSTAV SCHENK
Field Postmaster...."
Then the Number 20127 is 'Probably' the FELDPOST Number
.....Txs, Dave/dblmed