Yep, the system has lost contact with all of the sensors (either they've been removed or are done) but is still "looking" for them as the system hasn't been de-activated. My Laguna only has one sensor left working, so that same light is up to show that the others are not being monitored, and one tyre is showing on the car screen.
There's some way of deactivating the system by removing the fuse or something. I'm sure if you do a quick search you'll find it easy enough. The system will then be off, it won't be looking for any sensors, so the light won't show.