The New York Times and bloggist AdviceGoddess ran pieces on how air marshals are obvious because of the dress code that they have to adhear to.
From the New York Times: Federal air marshals must have neatly trimmed hair, and men must be clean-shaven, the documents say. Some of the service’s 21 field offices have mandated that male officers wear suits, ties and dress shoes while on duty, even in summer heat. Women are required to wear blouses and skirts or dress slacks.
Reminds me of spot the CID man at warehouse parties in Blackburn back in the day. They had a distinctive dress code of C&A and BHS easy care polyester clothing items that gave them away, while the drugs squad were the mad ones giving it a hundred and ten per cent in front of the strobe lamp.