I got told that:
 No flags or attachments - means driver is OK or could be unmarked cop car
 Green L Plate - newly qualified driver, liable to be obeying the speed limit
 Red L Plate - learner driver, liable to be obeying speed limit and using turn indicators
 One red cross on white flag - numpty driver, could be inebriated and liable to bursts of road rage at the mere mention of the Germans
 Two "red cross on white" flags - total ******** and obviously has more money than sense - liable to be driving 4x4 works vehicle and definitely stolen if seen on road during England match.   
 There is the poverty version of the flag going down the M62 every morning - it's a white ford escort van with a red cross stuck to the side made out of about ten rows of red insulation tape. 
