Ok, it's a just postwar picture, the headlamp rim, is a punched out blackoutmask, the Dutch did this a lot just after the war, as I have several of them.
LSK stands for? Schiet Kamp, sorry, I forgot, but I will remember. But the bike was used there, these numbers are not listed anywhere, but maybe Bastiaan knows more?
ISK was Infanterie Schiet Kamp, that was and is still located on the "Harskamp"
ASK was Artillerie Schiet Kamp, that was and is still located in "T'Harde"
Ok, I found it, it just means "Lucht Strijd Krachten" so Airforce in English, I found a picture, of 1950's BSA's, and some Volkswagens, I remember these, as I could have bought a couple 25 years ago, they were apple green!