From the Super Mario Wiki
WC 98 Kanbank.png

Kanbank is an enemy found in Wrecking Crew '98. It is the most dangerous enemy of them all, and is actually a sign of Bowser that is six walls wide and more than six walls tall, immediately ending the game of the opponent of the player that summoned it. It appears in combos of at least nine Pink Walls, and thus is very hard to get.

The message at the bottom of the sign, 安全第一 (anzen dai'ichi), means "safety first".