I have an Opton 85/2 with the same engraving. I have wondered if this strange engraving, in place of the red "T" had something to do with the copyright battle that was taking place in the early 1950s. If it is a misengraving, it is a very precise one. Really looks like someone intended to make an "F" given the unbalanced stroke at the top of the engraving- not at all like a balanced crossbar of a "T"