I'm the former Proteus employee, 1981-1993. Post some pix and I can offer some insight. ... never mind, i see them now. Must have looked at this quickly before that post above.

I am not sure what to make of your frame there. The decals are not what we did in house, Proteus never had engraved seat stay caps like those, The seat lug looks like a Prugnat S4 which we did use over many years of production, but the extra clamp ear reinforcement is very atypical, as are the suit of cards cutouts. We mostly did a mitered to a point seatstay attachment, and a good many fastback stays to a large machined binder. The Fork crown is late eighties Cinelli, but during my tenure, that's not one we used, though we sold them as an importer.

so... it is a "Proteus", but not one that came out of College Park MD from 1981-1993. Not sure where it originated.