Massassi One
After the Battle of Yavin, the Rebel Alliance employed the call sign Massassi One. While seeking a base and allies for the Rebel Alliance's, and on diplomatic missions, Luke Skywalker made use of it.
Behind the scenes
According to The Complete Star Wars Encyclopedia, Luke adopted this call sign; however, in Tatooine Sojourn, the character is conversing with Massassi-One, rather than identifying himself as such.