Couldn't you just buy a cheap printer with cash, use it, and then dump it as well, perhaps leave it in a charity bin somewhere.
Printers are pretty cheap these days, and it seems that in order for any of the markings to be useful they would have to find the printer in question in your possession/prove it was your printer.
An old dot-matrix or label / thermal receipt printer will do. Buy it at a Flea Market / yard Sale / hamfest / craigslist. Make sure you get a ribbon with it ;)
The more purchases they can tie to the event, the more information they have and the more chances to track you down. You can slip up at any point- for example, say you buy the printer at Best Buy, and they figure out based on the S/N which Best Buy and what day the sale was made. You can't turn off security cameras in Best Buy.
