Many wikis out there use icons, or artworks, to wiki layout and/or presentation. For example (my apologies, only french links provided):
One good start would be to investigate what kind of icons we would like to have in our wiki:
- any work previously done, or WIP, from TNF or marketing?
- define conformance to NetBSD's graphics standards?
- reusability? (licences, public domain vs CCs vs GNU derivative work, etc.)
Inspiration: see icons from wikimedia.