The Portal Gun Weapon Tags are 2 weapon tags (Orange and Blue) that are based on the game Portal. The weapon tags are exclusive to the Steam release of Blacklight: Retribution.
Portal Gun (Blue) Weapon Tag
The Blue Portal Gun tag can be bought from the Marketplace for 1337GP during the Steam promotion. It decreases recoil and max spread of your gun.
Portal Gun (Orange) Weapon Tag
The Orange Portal Gun tag can only be obtained by reaching Level 6 during the Steam promotion. It increases damage.