Ship Transponder/Transponder Code

The Transponder was a device that transmitted a ship's Transponder code. A Transponder code was a signal burned into the starship's sublight engines that transmitted the ship's name, type, owner, and other pertinent data. For most of the galaxy's history, the Bureau of Ships and Services issued and tracked transponder codes. 
Because a ship's Transponders are built into its sublight engines, it is difficult to remove or alter a ship's transponder code. However, there are two options: you can mask your ship's code (Making it impossible to read), or you can disguise your ship's code (Making it look like a different code). Some starships would mask their codes so frequently that they had multiple transponder codes that allowed the ship to have multiple identities.
The Identification Friend or Foe transponder, or IFF transponder, was an identity built into the core construction of every ship in the galaxy by at least the time of the Galactic Empire. It broadcast the identity of the ship to any other ship that came near enough. Altering this identity was considered theoretically impossible and it was also highly illegal to even attempt doing so. Despite this, many notable ships successfully defeated this system with the help of talented codebreakers.