At work, we use a Dymo electronic handheld label printer (
http://global.dymo.com/enGB/Products...Point_250.html ).
The nice thing is it has a sort of "count up" feature. Essentially, if you typed something like "PC0001" and pressed Shift + Print, the label would print, and the display would show "PC0002". Just keep pushing Shift + Print for each label.
The downside is that while the labels are difficult to remove, Students do manage it. But, it is easy enough to work out what the number should be by looking at the PC's next to it.