In this context 'patent' refers to the actual document (often a very formal letter) appointing a person an aristocrat. It will give the exact title and any conditions or restrictions, for example that the title can only be inherited in the male line. The patent also has the seal of the person making the award. In England only the reigning monarch could (can) appoint aristocrats, but in an outfit like the Holy Roman Empire the patent made it clear whether one's title was awarded by the Emperor or by a local prince, for example, or by someone acting on someone else's behalf. In England there are NO patents for the very oldest titles, and in a few cases there was much controversy about them, especially in Victorian times, when being an aristocrat was more classy than now.