They Live reference
During Keith David's Loyalty mission "He Lives", Roddy Piper attempts to beat sense into Keith David who is panicking about an alien invasion. Female Voice 2 (if not all of them) says "Put on the glasses Keith, we're not aliens". This is a reference to They Live, in which Roddy Piper tries to force Keith David to put on a pair of glasses that reveal aliens who are disguised as humans.