This tile, when placed on the floor of your base in the Sinnoh Underground in Diamond, Pear & Platinum, will send out a message informing the present users that the user is going to the Union Room when stepped on
Stepping on this Tool tells all nearby that you are going to the Union Room.
Episode 963 The Promise Between Ash and Pikachu
Episode 964 It is Time for Litten to Set Off!!