1:) QR Code By A Famous Cracking Group:
Right of the elevator to the C world you can see a bunch of QR codes. Look at who signed the bottom left one.
1:) Hidden QR Code:
From the floor 5, go out the window to the pigeons, then jump down on the left of to level 4’s roof instead of aiming for the star. From here jump again to the left and land on the roof of floor 3’s elevator. The QR code will be on the balcony on the right of the elevator.