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As far as I know, the coding of manufacturers began in earnest in the 1930's, so as to avoid the stifling conditions imposed by the Versailles Treaty.

After the Spanish Civil War intervention, "hidden production" ceased, but the maufacturers codes continued so as to avoid making war materials factories viable targets to the enemy.

I have not seen WW1 German gear with the makers codes like the WW2 stuff has, as I don't think it was as serious a security issue during the first War, due to primitive bombing technology back then.