When Valentino sent girls down the spring runways with calligraphy across their backs we thought, nice — beats a tattoo any day. Oh, for such innocent body art. First the Sphinx. Then the Swarovski. Oh, for the innocence of a Brazilian. This just in: Completely Bare has introduced a new service for girls who just can’t stop expressing themselves — bikini graffiti. What is it? Take a guess, but don’t think too hard. If stripping it all off leaves you feeling a bit, um, naked, Completely Bare will restore some modesty with well-placed words or designs applied in temporary ink that will last two to five days. With such a billboard, what kind of message could you send? “Proceed with caution.” (For the self-styled dominatrix.) “Your ad here.” (Very entrepreneurial.) “HAZMAT” (For the self-mocking.) “Please have package ready for inspection.” (Perfect for the pushy.) “This side up.” (For the directionally challenged.) “You must be this tall to go on this ride.” (Feeling playful?) “Employees must wash hands.” (No comment.) And you thought picking a signature lipstick was tough. Completely Bare, 764 Madison Avenue, between 65th and 66th Streets (212-717-9300); and 12 Chase Road, Scarsdale, NY (914-713-0200).