Despite years of reading monthly employment reports, this industrial category really jumped out at me for the first time this morning: "Lessors of nonfinancial intangible assets."
[WS:] http://www.census.gov/epcd/naics02/def/NDEF533.HTM
Prior to 2001 they were simply called "patent owners and lessors" (SIC 6794).
BTW, NAICS is a really good and detailed industrial classification system, far superior to other systems such as ISIC 3.1 (or even 4.0 soon to be implemented) or its European version NACE.
Wojtek