It certainly looks like a real Rossin to me.

I've got one also, without the usual Rossin-hallmarks except a panthographed fork. After lots of searching around for info, I came to the conclusion that not all Rossins have, for instance, a cut-out 'R' bottom bracket, the particular lugs and their name below the seatstay.

The earlier models (late 70's/ early 80's) certainly have those details, as well as the higher models after that period. But in the mid to late eighties, Rossin seems to have 'commissioned' quite some frames without those hallmarks. Usually it's on the mid to lower-end models; some of them might be even built for them, not by them per se. (But that was not that uncommon in that era, I've come to learn.)

Anyway, just my two cents: I wouldn't worry to much about it. It certainly doesn't resemble anything remotely suspicious (like some of the obviously fake frames with bad paintjobs and slapped-on Rossin decals, which is partly responsible for the general confusion, I think.)

I think it's a really cool frame by the way. Fantastic paintjob!