The acronym D.R.G.M. with or without punctuation stands for Deutsches Reichsgebrauchsmuster, meaning that the design or function of an item was officially registered inside all of the Germany states and not only locally registered as it was the case before the introduction of centralized registration. Note that many people quote this acronym as standing for Deutsches Reich Gebrauchsmuster, which is grammatically wrong and also omits the letter 's' after Reich. This results in shifting the weight of pronunciation on 'Deutsches Reich' alone, but this acronym has nothing to do with the Third Reich as many sellers want to imply so to catch the attention of certain 'collectors'. (German Reich Registered Design)
The D.R.G.M. signifies "Deutsches Reichsgebrauchsmuster" and is a design or use patent somewhat similar a "Registered" mark that provides an initial three years protection extendable for another three years to six maximum. D.R.G.M. registration was introduced and were first issued starting in 1891. However, if you are dating items you should hold in mind that even during Allied occupation up until 1949, registration procedures remained untouched and still used the D.R.G.M. registration documents, which of course explains why D.R.G.M. marks can be found on products actually manufactured up until 1952 as the registration itself was valid for three years. As from the end of October 1952, all registrations were definately marked with 'Deutsches Bundesgebrauchsmuster' (D.B.G.M.) or simply with 'Gebrauchsmuster' or 'Gebrauchsmusterschutz'.
As already noted, the D.R.G.M. registration offered a basic copyright protection for the duration of three years and included the right to indicate the item status by marking the registered items with the D.R.G.M. acronym. It was left to the registration owner to include the registration number as the D.R.G.M. marking alone was the element with legal character. The actual result of such a registration (the form of protection) was called Gebrauchsmusterschutz.
D.R.G.M. registered products were protected either for their way of intended use or design only and this did not include patent protection. Patent rights were secured by applying for a Deutsches Reichspatent (D.R.P.), so even if many people use the term 'D.R.G.M-Patent' it is factually wrong. Reason for this mix-up was that the D.R.G.M. registration in colloquial language was also known as 'kleines Reichspatent' which literally stands for 'small Imperial patent' but actually was meant as 'poor people's patent' and made fun of the fact that many manufacturers could not afford the fees needed to register a full patent. One should take into count that German patent registration fees (as was openly criticized during the year 1906) where two and a half times higher than in England - and 36 (!!!) times higher than in the US.
The acronym D.R.P. with or without punctuation stands for Deutsches Reichspatent which literally means 'German imperial patent'. Note that many people quote this acronym as standing for "Deutsche Reich Patent", an original and full patent with up to 15 years protection.
Such a patent registration was based on the 'Reichspatentgesetz' (German imperial patent law) which had been verified by the German authorities on May 25th 1877 after a long and hard struggle to introduce a set of rules and regulations since the first ideas for such a law had been discussed by the Prussian Borad of Trade back in July 1853. Even if it had taken 24 years for the German authorities to set it up, it's introduction was on extreme short notice as it was declared operational as from July 1st 1877, a mere month after its verification.
Of course such a unified patent law was quite spectacular at that time and so one would believe that the first patent itself would have been something special. But the first 'Reichspatent' was very unspectacular and was issued on the name of Joh. Zeltner who owned the 'Nürnberger Ultramarinfabrik' and had patented his method of synthetically manufacturing Ultramarine, a coloring substance that is still used even today. Patent 532 by the way was issued to Nikolaus August Otto and describes an extremely peculiar device named the 'Otto engine' - which of course is the anchestor of todays car engines.
It should be noted that many manufacturers could not afford the fees needed to register for a full patent. One should take into count that German patent registration fees (as was openly criticized during the year 1906) where two and a half times higher than in England - and 36 (!!!) times higher than in the US.