Cadillac 1993 DeVille Owners Literature page 183

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An OCTAGONAL (eight-sided) sign means STOP. It is always red with
white letters.
A DIAMOND-shaped sign is a warning of something ahead
-
for
example, a curve, steep hill, soft shoulder,
or
a narrow bridge.
A TRIANGLE, pointed downward, indicates YIELD. It assigns the
right-of-way to traffic on certain approaches to an intersection.