Ambiguous Signs Decoded

I thought the purpose of a sign was to make an announcement or instruct people how to act in a given situation. So what's the point of posting a sign that's completely ambiguous? I haven't a clue what it's supposed to convey--but someone else had an idea and was kind enough to spell it out for us (see below). Knowledge is power, which is why we should all know what to do the next time we set ourselves on fire.

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