Ambiguous Visual Sign of the Week

A word of introduction. Over the last 30-40 years visual signs have become ubiqutous in modern cities all over the world, much like traffic signs. I think it took off from airports. The idea is that these signs are self-explanatory and therefore require no knowledge of local language, they are cross cultural etc. But lately i begun noticing how ambiguous and sometimes downright stupid these signs are. Over the next few weeks i'll give some examples.

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What does this sign mean?

a. Do not put your hand in the hot tarmac
b. No admittence to unauthorized personnel
c. No gloves allowed on site
d. Abusive behaviour to our staff will not be tolerated

(correct answer is in the comment section)