Warning signs

A warning sign is a type of sign which indicates a potential hazard, obstacle or condition requiring special attention.

Non-traffic warning signs
Warning signs are also found on other potential dangerous sites. At the base of electricity pylons or fences of substations or radiotechnical equipment with open parts leading high voltage, there are signs warning of high voltage. Warning signs can be found at the top of inclines. "Beware of Dog" is a typical warning of the presence of a dog, but there is no standard sign design.
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https://en.wikipedia.org/wiki/Warning_sign