Williamsburg - Resident Leaves Note On His Artist Neighbors Door

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Williamsburg artist came home to find a sticky note put up outside the door of his apartment. Can anyone tell him what this means? Or even what language it is in?

Similar notes were stuck next to other apartment doors in his building as well. One outside each apt door on the second, third, and fourth flood, and one next to the ladder to the roof, and some were on the first floor.