thought it was L&L but not sure
"Many of the things built by the architect and freelance designer Bergholt Stuttley ('Bloody Stupid') Johnson were recorded in Ankh-Morpork, often on the line where it says 'Cause of Death'. He was, people agreed, a genius, at least if you defined the word broadly. Certainly no one else in the world could make an explosive mixture out of common sand and water. A good designer, he always said, should be capable of anything. And, indeed he was."
A poster outside one shop urged people to Dig For Victory, as if it were some kind of turnip.