Originally Posted by travelinmanS
I was in Guangzhou walking back to my hotel with my girlfriend last night and two cops came up to us on the sidewalk and asked to see our passports.
Upon reading your most recent post, I just got another idea. They might have been checking to make sure you weren't on Shenzhen only visas. Some Taiwanese friends were visited factories in Dongguan two weeks ago and received the third degree when they tried to leave Shenzhen (at one of the checkpoints) because they didn't have their passports.