Hi Roland,
http://www.luftwaffe-experten.org/stam-wl.html
Here, only WL-xxxx four letters (Total six letters)
Hence could be WL-LNOS
or here:
http://www.luftwaffe-experten.org/d-letters.html
only D-xxxx four letters (Total Five letters)
Hence could be D-LNOS
or GL(?)-LNOS (?)/GL-NOS don't know this kind of code so no "could be", at least for me.
That's the reason I did, at last, prefer put ?L+NOS as it appears on picture instead of conventional way to write these codes.
Regards, Franck.