:hi: Paul,
SG stands for Sächsische Glasfabrik, Radeberg, from around 1932 owned by Walther Glas (AWS in heart)
Your mug appears in Walther Seidel-Katalog 1935, page 22
*Tübinger Walzenseidel*, gewöhnlich (common) or schwer (heavy) - mould no. 1210/11 height ca 107
I do not know what B stands for - the catalogue speaks of K and H only - may be a mark for export?