Looking through the whole set, it's obvious that (a) some are the first installation; (b) some have been replaced by newer tilings; and (c) some have been preserved -- particularly Leary Ave (which is outside the Canal Station condos) and Wilbert St at 24th Ave (which is outside the NoMa condos). And a few are missing here and there: Ship St. signs don't exist for 20th Ave., Times St. signs aren't on 24th.
If you know of any other signs, I'd be happy to go take its picture and add it to the set. There is a sign for 24th Ave., at Ballard Ave., but I think it's a more recent addition: it's larger and black and white, not blue and white.
Now what? That's the question.