Funny how the historical meaning of the Directory Opus' icon seems like an indecipherable symbol nowadays
I think that the Opus' icon is a composite of a lightbulb (that yellow circle with stylized rays radiating from it) and a metal slider-cover of a diskette (also acting as a bottom of the lightbulb). Diskette obviously from the Opus' past of file managing, but the lightbulb I think is from the old Inovatronics Opus days where there was a lightbulb motif if I recall correctly (innovatronics -> innovation -> idea -> lightbulb symbol, and also the "tronics" part which implies electricity). I might be wrong though.
Btw this same icon we're having now is from Directory Opus 5!