Buick 1993 Skylark Owner's Manual page 142

Shape of Road Signs
The shape of the sign will tell you something, too.
An OCTAGONAL
(eight-sided) sign
means STOP. It is
always red with white
F
ST0 P
1
d
letters.
f
I
A DIAMOND-shaped
sign is a warning of
something ahead - for
example, a curve, steep
hill, soft shoulder, or a
A TRIANGLE, pointed
downward, indicates
YIELD. It assigns the
right-of-way to traffic
on
certain approaches
to an intersection.
A TRIANGULAR
sign also is used on
two-lane roads to
indicate a NO
PASSING ZONE.
This sign will be on
the left side of the
roadway.