In one sense, this is just a sign on the WoodenBoat School campus at the crest of an unpaved private lane, where large fields are to its right and left. (See below.)
However, its unusual appearance sometimes provokes an urge to consider it just the first word in a warning or advice:
SLOW Saint Peter Ahead, or
SLOW Fawns Playing, or
“SLOW But Steady Wins the Day” (Aesop).
(Brooklin, Maine)