The Block Changer sign can change the types of blocks displayed in a minecart. For example, a storage minecart shows a chest - here the displayed block type is a chest. You can change the type of block from a chest to something else using this sign. All minecart types support this sign, and the displayed block types are persistent through server restarts.
方块更改器可以更改矿车中显示的方块类型。比如，储存矿车内显示的是一个箱子 - 那么显示的方块就是箱子。