Passing through the newly re signalled Wolverhampton the other day got me wondering. In 'existing' signalling setups - PSBs, lever frame boxes etc - the origin of the signal prefixes is usually the box name, Wolverhampton was WV, Gloucester is G etc. The new signals at Wolverhampton are WS xx and BS xx. I'm sure there's a logic to the labelling but what it is eludes me...can anyone enlighten me?