What the title says .... Just leaving today from PEK and noticed signs up for the "D" gates, being used now for some domestic flights.

The T3-shuttle trains at the moment at least are running some trains going direct to T3E, and some only going to T3D, so you may need to pay a little extra attention if running to catch a train about to leave).

Access to the D gates is through the usual international departures lanes - though now they have installed automated gates that require you to scan your boarding pass.