The Easter egg in the Saints Row reboot refers to the End of the Line mission from GTA San Andreas, in which CJ and Sweet defeated Big Smoke and Frank Tenpenny. Officer Tenpenny witnessed Big Smoke's death and tried to get away with his money. The antagonist failed to control a fire truck and went off a bridge in the Ganton area.
A Saints Row character also falls off a cliff in a truck. He lies on the ground and says, "end of the line motherfucker." This is a direct reference to the title of the final mission of GTA San Andreas.