A class 2 signal was a type of communique used between starships in which the sending ship requested the surrender of the receiving ship.

After the USS Enterprise became surrounded in the Romulan Neutral Zone by three Romulan battle cruisers in 2268, Sub-Commander Tal of the Romulan flagship sent the Enterprise a class 2 signal, stating, "you will surrender immediately, or we will destroy you." (TOS: "The Enterprise Incident")

Following the 2269 disappearance of the IKS Klothos in the Delta Triangle, Kuri, the commander of one of her sister ships, sent a class 2 signal to the USS Enterprise demanding their surrender. (TAS: "The Time Trap")