GMC 1993 Safari Owner's Manual page 161

AM402009
A TRIANGLE pointed downward, indicates YIELD. It assigns the right-of-way
to traffic on certain approaches to an intersection.
I
AM40201
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.
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RECTANGULAR (square or oblong) signs show speed limits, parking
regulations, give directions, and such information as distances to cities.
AM402011
KEEP
RIGHT
LEFT OR
THROUGH
RIGHT TURN
ONLY
4-5