Deadhead? Or just positive space for training. Either way you can check in at gate (domestic) or check in on your smart phone usairways.com or United.com . It'll give you a eScan boarding pass. If you're heading to Kobenhavn (CPH) or Toronto(YYZ) for a train event your probably gonna want to do counter and gate for "passport control."

If you're completely unsure, not in uniform and going thru regular security lanes then print off a boarding pass at the kiosk before you head thru security.

Deadhead once "on-line" and in uniform?....pssshhhh, just show up at the gate and pick up your boarding pass typically.