This is usually affixed with transfer paper, similar to the printing paper I played with when I was a kid. The required models, specifications, trademarks, etc. are printed on a transparent plastic film in advance. After the belt is produced, it is directly affixed and then the plastic is put on it. The film is removed and the words are left on the belt. Of course, there are also intaglio letterings on the belt, usually flat vulcanized belts. Most of the time, the words can be made directly on the mold.