Bath et Well is the traditional episcopal signature of the bishop of Bath and Wells. For more details on traditional Latin abbreviated signatures, see Cantuar, which describes the case for Canterbury. The sad thing is that Bath et Well stands for Bathomensis et Wellensis, which is only Latin for 'Bath and Wells' if you think that Latin starts in about 1450. Aquae Sulis et Fontes would be far more accurate, but I imagine that bishops would be slightly wary of signing with the name of a pagan goddess - Sul.