GMC 1994 Yukon Owner's Manual page 8

Safety Warnings and Symbols
You will find a number of safety cautions in this book. We use a box with
gray background and the word CAUTION to tell you about things that could
hurt you if you were to ignore the warning.
In the gray caution area, we tell you what the hazard is. Then we tell you
what to do to help avoid or reduce the hazard. Please read these cautions. If
you don't, you or others could be hurt.
You will also find a circle with a slash through it in this book. This safety
symbol means "Don't,'' "Don't do this," or "Don't let this happen."
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