LONDON (January 18, 2013)—Stephen Graham, 47, a British professor who specializes in cities and urban life was convicted Friday of damaging luxury cars with graffiti that was surprisingly polite.

Graham was found guilty of using a screwdriver to scrawl inoffensive words such as "very silly," ''really wrong" and "arbitrary" into the paintwork of vehicles including a Mercedes, an Audi, and a Volvo.

Prosecutors said the spree caused about $29,000 in damages.

Graham, who teaches at Newcastle University in northeast England, pleaded guilty to criminal damage at Newcastle Crown Court.

Graham's lawyer said the academic had no recollection of his August vandalism spree.

Graham previously blamed a bad reaction to alcohol, antibiotics and prescription drugs for his behavior.

Judge James Gos said he would sentence Graham next month.