Help with German gasmask markings

[Feuerbach]

I was just reading the very interesting thread on the Gasmaske Behalter with the Paris label, and thought; I have a question myself on one of mine Behalters.
Can anybody tell me something about the painted markings on the can? It reads; 428/S. Would that be the Feldpost number? Or is that a 5 digit number? Has it something to do with the regiment, and if so is there any of telling what regiment it belonged to?
I think it's a M38 model, (or maybe it's a M30?). I picked it up last year at a car boot sale, and it's nearly complete, but missing the inside small box for the spare glasses. Guess somebody ripped it out one day, but beside that it's in very nice condition I think. It has a leather strap around it dating 1941.
Thanks for any input!

[GIZMO8Z]

I may be totally off, but if I remember correctly, the painted numbers represent that specific gas mask's number. For example, if your gas mask was among a batch given to a group of 500 troops, yours would be 428 out of 500.

I hope someone with more experience can clarify!