What does SRVNA stand for ?

There is one of these pitches at Grafham Water, along with 9 other serviced pitches. This pitch had a sign on it saying 'prebooked only', which seemed a bit odd to me, as none of the other serviced pitches were marked in this way. It also had a traffic cone placed on it, which was moved after a few days when a van arrived and pitched there.

When we left, I asked the warden what SRVNA stood for, and he told me that it was a serviced pitch without awning, and that this could be booked via the CC website. As there is only one pitch fitting this description, it implied that you could book a specific pitch. However, I've just double checked the booking page, and there is only an option for serviced pitches, not 'SRVNA' pitches.

Not bothered, just curious.