So, here's my question. How will city guards feature in-game?

I haven't seen many videos and stuff, but has any clue been given out? I wonder whether they will have a completely passive role, for instance just giving instructions, or they will actually serve the law, chasing any thieves. There will be a thieves guild, so there will be a prison too. I also wonder whether we could join the guards, as a rival faction to the thieves guild.