I find that a backpack is such an easy way to go about my day, but I'm concerned about being a target for thieves. Is this just asking for trouble? I would keep my valuables under my clothes and just put non-essentials in the backpack.
Are you asking about a true backpack or just a small day bag.? Small day bag, shoulder bag, messenger bag, etc. is fairly common for a lot of tourists. That will not, in itself, make you a target. However, how you handle the bag in crowded situations does have some impact. How much stuff are you carrying during the day that would require a backpack?
Men and women carry messenger bags, which work well for days ou and about.
I prefer a satchel (Indiana Jones had a satchel :) )or messenger bag. I have seen to many videos of peoples backpacks being broken into while standing in a large crowd or waiting to cross a street full of people. Its amazing how people don't feel someone entering their bag and taking out items. And for those that turn their backpacks around and where them on their chest, what's the point.