The Uni-Ball PWE8K Pack of 6 Thick Chisel Tip Chalk Marker writes on and wipes off, making it the perfect tool for sign writing on non-porous surfaces such as chalkboards. It is rain-resistant, so your message will hold up outdoors, but the ink is water-based, so if you want to remove it, simply wipe away with a damp cloth, or a little mild detergent if stubborn.