Both portcullises are made of iron and each has the inscription "A+B" and an arrow pointing upward on them. Looking through the bars of each portcullis, from the inner west portcullis, you see that a 10 foot wide corridor leads west for at least 30 feet before trailing off into darkness (30 feet is how far torchlight goes). From the inner east porcullis, you see a 10 foot wide corridor going both south and east for at least 30 feet before trailing off into darkness.
Each of you take a turn listening to each of the doors. No one hears anything from the west door, but Devin, Rondo, and Bertrem all hear the rattle of chains behind the east door.