Carl Biggs, regional manager of 11 Arby's restaurants in Chicago's Northwest suburbs, has done all he can here, the 41-year-old announced Monday before vanishing from the chain's Rand Road outlet in a cloud of Ford Escort exhaust. 'Who was that mysterious man?' asked awestruck cashier Doug Sowell, 19, shortly after the visit. 'I don't know,' crew chief Karen Wilhoyte responded, 'but he left this memorandum detailing proper kitchen hygiene procedures.' 