The eight signal towers atop Soulforge Cathedral are used to send messages to all Masked Servants within range. They can be attuned to either "signal slot A" or "signal slot B", transmitting Karras' instructions or the return command, respectively[1]. The tower itself resembles a miniature high voltage tower topped with three copper tines. Each tower is positioned in an isolated patch of roof, the entryways indicated by the sign below.
Despite Karras' warning, the signal towers do not need to be switched back to signal slot A in order to allow his signal to be heard. The Masked Servants will release the Necrotic Mutox even when most or all of the towers are set to signal slot B.
Map showing the locations of six Signal Towers