previous work is fine in this case. but i worked at a place that was a pita to release open source code, so i learned to always work open source anonymously.
i wouldn't want to break that anonymity. also, i already had the displeasure of having a candidate turn his laptop to me and show his great coding a skills with a competitor online app store (yes, a major brand app store source), and i had to get involved in all sorts of annoyance from HR and legal. maybe I'm just dumb for taking those things seriously... but i think that's for the better