Basically its about confidence, cops walk around the street confident and they act confident in all that they do as a cop, fireman act confident when they rush into a burning building. Ots bassically linked to confidence. The uniform has something to do with it too, but the reason i believe women find uniforms sexy is because the men who have worn a uniform throughout history have been confident people often risking their lifes for what they believe, so the uniform thing is deep rooted in a womens physc.