As was the case with the first Blockbuster challenge, completion of all Week 2 challenges unlocks a new loading screen:
Seen on the wall behind Omega are markings that read ‘A4’, ‘B4’, ‘A3’ and ‘B3’ which are coordinates. If you visit the location in between these squares (shown on the map below), you’ll find a free Battle Star to pick up:
Note: You must have already completed all the challenges for Week 2 to be able to retrieve this star.
SOURCE: Reddit – Credit to Bfor45 for the images