No evidence is available for this source.
There are certain structural similarities between the Arch of Trajan and Arch of Titus but in general far more sculpture on the former, with large figures right up into the attic portion of the relief. The inscription is also especially large and clear on the Arch of Trajan. We can presume that letter-carvers were specialist workers, as they usually are today. Letter carving is mainly done with the flat chisel with a good square corner to achieve a sharp angle.