There's at least one backplane signal, usually 3 or 4, and they are AC. The typical one with multiple signals uses an odd stepped voltage arrangement that used to be called something like "Pelt and Ashko multiplex" (anyone remember this?), but I can't find the reference on Google. Here's what the signals look like -
**broken link removed**
DC can kill the LCD, so can a high voltage. However, the LCD frequency is pretty liberal, and will work at 60hz. So if you get a small transformer that puts out about 3V, you can use this to activate segments if you just want to goof around with it like that.