No sign

The no sign is a special tile tool introduced in Chip's Challenge 2. It typically must be placed on top of a key or boots, though it is possible to place them independently using external tools. The no sign is an acting wall to Chip, Melinda, mirror Chip, mirror Melinda, any monster, or any block if they have the key or boot in their inventory which is underneath the no tile. While ghosts and rovers are the only monsters that can carry boots, blue keys can be picked up by all monsters and dirt blocks, and thus a no blue key tile will apply.