Crossword puzzle clue "one barely seen"

One barely seen!

Spiro who wrote, "If you've seen one city slum, you've seen them all"

"If you've ___ seen a one-trick pony, then you've seen me"

Ones who can barely be seen?

Springsteen "If you've ever seen ___ trick pony then you've seen me"

Feeling that you've seen something before seen something before

"If you haven't seen ___, you haven't seen New York" (old ad slogan)

Something often seen on a street corner, briefly ... or, literally, something seen in each corner of this puzzle