Minecraft wiki entry for Glazed_terracotta_patterns, associated text: Magenta glazed terracotta has an arrow that points in the direction the player was facing when it was placed. This can be used to share the different rotations of terracotta pattern. There is a single-color and multi-color example below. On one layer, there is the pattern, and the second layer has the magenta terracotta "key," which tells the player which direction they should face when placing the terracotta blocks.