Based on those Caution wet floor signs, this one warns about the bisection hazard from lurking ninjas.
Not sure what you'd call this kind of sign. A free-standing sandwich board? A reversible sign? A fold-flat accident prevention sign? Anyway, whatever this is, feel free to put your own information on it. Just a matter of editing the texture.
Like this model, but need something a bit different? I take commissions! http://peripheralarbor.com/commission/