72nd and Broadway      "Nobody, but nobody," reads the sign outside Gray's Papaya, "serves a better frankfurter." People seem to agree, as Gray's Papaya has been a perennial favorite since it opened in 1972. Their delicious hot dogs are considered the best in the city by discriminating New Yorkers, who also stop by Gray's for a wide variety of fresh-squeezed fruit juices. With no place to sit, Gray's still pulls in crowds of patrons, probably because their hot dog prices -- $.50 a piece, "no gimmicks, no bull," according to signs inside -- haven't gone up since, well, as long as anyone can seem to remember. (While they did charge $.60 and $.75 for brief periods, two hot dogs for a buck seems to be back for good.)      In true New Yorker fashion, owner Nicolas A. B. Gray isn't afraid to express his opinions: large signs outside the store (and its downtown counterpart) declare "Hang in there, Mr. President!" Gray's is also a vocal supporter of Mayor Rudolph Giuliani's "fight for a nicer New York." "Toujours la Politesse!" reads the sign. Patrons and passersby are also asked -- politely, of course -- not to "expectorate on our sidewalk." Rudy would be proud. Don't miss the "Recession Special" -- 2 franks and a drink for $1.95.      Also the house mustard tastes like a good dijon. next: Verdi Square