It's on their website and stupid but it's in-line with the no shoe rule in general. I have a pair of slipper socks (non skid underneath) that I use and put them in a plastic baggie on the other end. Each pair gets one walk thru and then a hot water washing. Those floors are just disgusting.

On a side note, BWI was where the TSO pulled my baggie and told me it was "too full". Called over his supervisor and after they discussed the baggie told me that I would be allowed to go through with it "this time", but the next time my bag would be confiscated. As the baggie was far from being as packed as it usually was and the stuff could be moved around easily I was really OTOH, it was 6 am and I was just too tired so I asked for the guys name and left a complaint the next day when I came through BWI on the return.