Make no mistake about it, this city has to be the most conservative city I have ever experienced and I ve travelled to almost every Middle Eastern country. Female travellers should wear a headscarf (I highly recommend it) because not only are the women in this city covered up but they wear the Afghan style burkas making you feel as though you are in Afghanistan rather than Pakistan. Men shouldnt wear T shirts or shorts and the local gear is brilliant with trying to blend in with the local men especially when you walk around the bazaar. Overall, Peshawar is deeply deeply conservative and your dress should reflect the fact that you are a visitor in a deeply conservative society.
One of the most striking things to me was the different dress in Peshawar compared to other cities of Pakistan. Most men I saw on the streets of the actual city were bearded, and rarely did I see a woman's face go uncovered. Thus, I would reccomend even more modest dress than usual in Peshawar, especially for women.