Instructions
Start your game using the character who originally placed the sign. You cannot remove a sign that was not placed by your active character, including signs placed in towns that you visit and the wooden signs used to mark the spot where an animal's house may be built.
Walk over to an outdoor sign and stand over it. Press the "B" button to pick up the sign and place it in your inventory.
Stand next to an indoor sign and press the "A" button to move or rotate the sign. Press the "B" button to place the sign in your inventory.