The fork crown, seat stay terminations at top, seat/top tube lug and bottom bracket lug are not "crude" but don't look like those of a higher-end bike. Another clue to the quality/buttedness/lightness of the tubeset is the (proper) diameter of seat post that the frame takes. Yours looks appropriately sized, based on the slot at the rear. None of these factors will indicate a manufacturer, unless they're very distinctive (not the case for this frame, I think); but they do indicate frame/build quality.

Don't be disappointed; I commute on a frame that has no obvious "cachet", but it's very well constructed, and I enjoy it for that. Other frames have a better ride and pedigree, and are one or even two pounds lighter, but this one is special too. It has a "stately" presence. People love their old Raleigh 3-speed models and Lentons, even though they were not the cream of bicycle offerings in their day.