tagging

I came across this sign in the stairwell of a building yesterday, and am still not sure what it means. All I can think of is that they've had problems with obnoxious children chasing each other up and down the stairs and screaming, "YOU'RE IT!!" If any Chinese readers out there can fill me in on other possible interpretations, I'd be much obliged.

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Update: My friend Kristi informs me that "tagging" can refer to graffiti, or a special style of graffiti. Thanks, Kristi!