Class 2 signal

From Memory Alpha, the free Star Trek reference.

A class 2 signal is a type of communique used between starships where the sending ship requests the surrender of the receiving ship.

After the USS Enterprise became surrounded in the Romulan Neutral Zone by three Romulan battle cruisers, Subcommander 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")

After the 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")