Other than a radioactive glow?
Obvious things, like wearing red. I mean, that's so logical I hardly need to explain it, but basically what they did there in that study was show pictures of men to 288 women, Photoshopping some of the men's outfits to red. When women saw the guys in red, they rated them higher in terms of power and sexiness, but not in likability, kindness, or social skills, because who cares about that. Tying red to power and success even crosses cultures, having that meaning in places as diverse as China, Japan, Africa, and ancient Rome.
How is that any different from men, you might ask, since we all know that men are also attracted to women in red? Well, in that study, seeing a woman in red caused men to ask the women sexier questions (or plan to ask them -- the researchers made sure to keep the test subjects well away from the women), which implies they find her more attractive, or more receptive, or both. But not more powerful.
"Powerful" isn't the word I would use here.
One popular study that might be confusing here is one that showed that while women say they value earning power and ambition over looks, their actions indicate all those factors are about equally important, with a slight edge to looks (but more on that in a moment). So one set of scientists has to be a pack of liars, right?
"Wh-why would you say that?"
As the red study shows, there's obviously at least one subconscious visual clue that makes a woman think a man is more powerful, and there's surely more (distinguished salt-and-pepper hair perhaps?). So when a woman is evaluating a man on "looks," she's partially evaluating him for other traits like power and wealth (and personality sometimes, we're not all shallow strumpets), even if she doesn't know it.
As an example, think of male strippers.