Use 3-sided tomato cages to make signs to stick in the ground.

If you're having a yard sale or just want to make a sign, an easy method is to use 3-sided tomato cages that fold flat. Unfold the cage and put your sign inside. Tape it in place across some of the wires to keep it from sliding up-and-down then fold the cage sides back onto the surface to keep it locked in place.