Urban witchcraft is basically for when you live in a city. It's kind of like urban animism, as far as I've seen. Instead of working with nature, you work with the city. Graffiti is how you can find your daily "signs", crossroad spirits (the lwa Papa Legba is one such famous spirit), etc. You do your witchcraft with things easily found in the city or home. I've seen some use office supplies as tools. :b Use what you got, etc.
@Octavia- Techno witchcraft is about using the modern machines in your work. Using the games Sims for your poppets, using Animal Crossing for your shrines and altars (something I'm totally going to do <3), using apps as a part of your spells (e.g. if you live on campus you can't burn any candles - so they'd use a Candle App), and when coding their tumblrs/websites, they'd include a sigil of their own making within the code.