Thanks to Google's patent search page, I found this filing from May 7, 1998, granting Jerome M. Kurtzberg and John Stephen Lew from IBM a patent on a "Visual Display for Music Generated Via a Electric Apparatus".
The device is similar in principal to Fred Nachbaur's BAMTRAT project or the visual tone indicators on the Terpistone dance theremin.
It will take me quite a while to pour through all the other theremin-related patents I turned up on my search. A few that pop out include: a theremin-based soap dispensor, Raymond Scott's patent for a keyboard controlled theremin, and a theremin-controlled mattress.
