Regarding Pisanello's impresa, I think that here are much better analogs to trademarks, and they predate imprese: such are the merchants marks of Northern Europe, and of course coats of arms everywhere in Western Europe. Since the 14th c. goldsmiths and silversmiths were required by the statutes of their guilds to put their makers' marks on their works.

Mint marks for individual mint-masters, which appear roughly at the same time, are similar. Arguably their purpose was different. But the concept of trademark was more general, including its legal aspect.

The great jurist Bartolo, in his tract "de insignis et armis" (unfinished at his death in 1357), gives several examples of trademarks, such as the watermarks of paper-makers or marks of sword-makers, and explains why they ought to be considered as protected by law against counterfeiting, even discussing who owns the trademark when a partnership is dissolved. Going farther back, one finds trademarks imprinted on Roman bricks and amphorae by their producers.

Dick Johnson says that the trademark symbol is a T in a small circle. In fact, it is a small TM, or -- for registered trademarks, an R in a small circle ®.