In Dark Souls, what item is used to summon another player for cooperative play?

In Dark Souls, the White Sign Soapstone is used to place a cooperative summon sign.

A player uses the item to write a glowing sign on the ground in another player’s world. A host can then interact with that sign to summon the sign’s author as a phantom for cooperative play. The summoned player helps defeat enemies and usually disappears after the area boss is defeated or the phantom dies.

Solaire of Astora gives the White Sign Soapstone early in the game, making it one of the clearest introductions to Dark Souls’ online systems. The item supports the game’s unusual mixture of isolation and indirect multiplayer, where messages, bloodstains, invasions, and summon signs appear within otherwise single-player exploration.

The White Sign Soapstone should not be confused with the Red Sign Soapstone. The red version is associated with hostile player-versus-player duels, while the White Sign Soapstone is primarily a cooperative tool. The Black Separation Crystal dismisses a summoned phantom rather than creating a summon sign.