A Badass or criminal character will often dress conservatively (suit and tie) to imply that he is a "professional" who knows what he is doing. Generally partakes of a toned-down version of Badass Longcoat imagery; add Cool/Sinister Shades to complete the look. The suit will usually be impeccable.
This trope can include women who wear traditionally male attire (read: suits), with the further implication that they are tough enough to make it in a man's world. If the writer doesn't want the female character to wear traditionally male attire, a pencil skirt has the same implication of professionalism especially when paired with a suit jacket. But, it isn't really a Distaff Counterpart.
One easy way of showing that a situation is getting worse or dangerous is to have the previously immaculate suit become messier somehow, generally with bloodstains or just having any unnecessary bits such as the tie or jacket taken off and the sleeves rolled up.
Of course, there's a reason why suits are THE sign of masculinity (and everything associated with it). It's because they look really nice on men. Thus male characters will sometimes be put in a suit for no particular reason other than aesthetics. That is not this trope.
Be aware that in Period Piece works, pretty much all the male characters will wear suits (unless their occupation has a uniform associated with it), so the suit won't qualify as this trope. Often some other piece of clothing will be used for the same purpose as this trope instead (bowler hats, bowties, and pocket watches are popular choices). There are a few careers in which this style of dress ranges from common to near-universal: The Men in Black, Wicked Cultured Professional Killers (especially if they are Bantering Baddie Buddies), Corrupt Corporate Executives, Corporate Samurai, Amoral Attorneys, many Battle Butlers and yakuza/mafiosi.
This trope does not cover flashy or eccentric suits worn as a fashion statement. The suits are supposed to be something you would wear at work. Therefore, Spike Spiegel's and Lupin's respective blue and red leisure suits don't quite count. Jim Carrey's shoulder-padded yellow getup in The Mask is about as far from this trope as you can possibly get.
A Sub-Trope of Stock Costume Traits and Sharp-Dressed Man.
Compare Sharp-Dressed Man, Tuxedo and Martini, Villain in a White Suit; Coat, Hat, Mask; Man of Wealth and Taste; Battle Ballgown; Kicking Ass in All Her Finery. See also: Lady in a Power Suit.
