The trademarks were protected. They were protected under the Paris Convention for the Protection of Industrial Property of March 20, 1883.
Pete
If you care for googling "Marke Monopol", German for "monopoly trademark", you will get about 290 000 results. "Monopol" stands for a long established line of household tools, probably as old as that Drilling, a tobacco company equally old, a razor/cutlery trademark from Solingen, a jeans company and so on. There also was a coalmine named "Zeche Monopol", founded 1891, in Bergkamen, near Witten. Trademarks were only protected for a specified group of products, so one company may use it for household items, the next for razors, another for tobaccos and so on. So, even if Francotte registered "Monopole-Liege" some time, as spelled in French on the gun, other gunmakers were free to use "Monopol Drilling" on their guns. Even if one gunmaker had protected Monopol for his guns, the Witten steelworks still could register it for some sort of steel. It may even have been the other way around: As "Monopol" already was a popular German trademark at that time, Francotte quickly registered "Monopole-Liege"in Belgium to get an advantage in the German market.
And, even if Francotte (btw, which one? There were 7 gunmakers of that name in Liege!) registered "Monopol" in Belgium, it was left to the courts if this registration had any priorority and was valid in Germany. Apparently all companies using "Monopol" shied away from lawsuits for good reason.
