Number on L strap brass buckle

Can any one advise what this number might mean.  I have viewed or studied dozens of L straps over the years and have never encountered this kind of number.  It must be some kind of production number but who knows.   i have had to over expose the picture to bring out the number but please take a look.  Thanks all.

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Registered patent number I expect. No, I haven't seen that stamped before and it seems excessive given the number of these produced under wartime conditions. Is it British? Canadian? Other?