So, you want a job in the C-suite? Let's talk about your image.

Landing a leadership role in banking takes years of experience and an impressive resume. But it also takes poise, polish and the ability to captivate a room. Think of it as stage presence for the business world.

In an effort to groom their top talent, some of the industry's biggest firms are offering training sessions on how to look and sound like a powerful executive.

But how do you tell Ivy League MBAs they need to work on their image?

"Very, very carefully. Let me tell you," said Stanley Zareff, an executive coach in the private banking and wealth management division at Credit Suisse.

Through a combination of personal consultations and professional workshops, banks are teaching the art of "executive presence."

It is a je ne sais quoi that is easy to spot but difficult to define. It is corporate star power. It involves a combination of gravitas, communication skills and personal style.

Sylvia Ann Hewlett, chief executive of the Center for Talent Innovation in New York, wrote a book on the subject in 2014.

"Executive presence is not a measure of performance: whether indeed you hit the numbers, attain the ratings or actually have a transformative idea," she wrote. "Rather, it's a measure of image: whether you signal to others that you have what it takes, that you're star material."

It also plays a big role in hiring decisions, accounting for 26% of what it takes to get promoted, CTI said in a 2012 report on the subject.

American Express recently began offering executive presence seminars as part of a women's empowerment initiative.

Valerie Grillo, the company's chief diversity officer, said that the company began offering the trainings as part of a broader initiative to get women into senior-level positions throughout the company. In talking with managers about why women had been passed over for promotions, she often heard vague critiques.

"We would hear things such as this person is not clear, or this person does not look the part," she said.

Grillo said the conversations reflected research findings — that when it comes to high-level promotions, managers are often more critical about whether women fit the right image.

"Look, there's a double standard," she said.

Andrea Turner Moffitt, a senior vice president at the CTI, echoed Grillo's concerns in a recent interview. "Unconscious biases often manifest themselves in terms of executive presence," she said.

So Amex began offering trainings as a way "to get a common language" around the attributes of influential leaders, Grillo said.

In two-hour workshops, women employees — usually young MBAs — watch videos of well-known executives and political leaders. They discuss the importance of communication style and body language.

"It can be a bit personal," Grillo said.  

Amex, along with many firms, does not emphasize the importance of appearance in its executive-presence trainings.

But Hewlett, the head of CTI, pulls few punches on the topic of personal style in her book, arguing that careful attention to fashion can signal to employers that you have what it takes.

"A judicious use of cosmetics, neatly manicured nails, well-fitting jeans (Silicon Valley), a perfectly cut jacket (Wall Street) and carefully coifed hair make all the difference," she wrote.

Deutsche Bank and Credit Suisse both offer a range of options for executive presence training. For high-level executives, in particular, they offer more personalized sessions that include professional acting coaches.

Leaders from across the globe at Deutsche work one-on-one with Patsy Rodenburg, a theater coach and Shakespeare expert who has worked with Academy Award-winning actors, including Judi Dench and Daniel Day-Lewis.

Many of the trainings have a performative aspect to them, according to Nisha Rao, Deutsche's head of talent and development.

"The participants are asked to present or tell a story that is relevant to their work, and they get real-time feedback," she said.

The ability to convey both authority and clarity is necessary for leaders in the banking business, she said. "Ours is a relationship and advisory-oriented business. Inspiring confidence and earning the trust of our clients and our employees is a key expectation."

At Credit Suisse, executives work on refining their image with Stanley Zareff, a professional acting coach who works full time in the bank's communications department.

Zareff said in a recent interview that he often introduces himself by saying this: "Let's cut to the chase, I'm here to make you look good."

Zareff preps senior managers for employee town-hall meetings. He also provides suggestions for shirt-and-tie combinations before executives appear on CNBC's "Squawk Box."

"You want that senior presence, you want that power presence," he said, noting that he often has to tell people to pull their shoulders back.

Additionally, Zareff provides advice on personal style to employees who have received executive promotions. He described a recent consultation with a woman who was about to be promoted as a managing director. She had a reputation as being "very hip" and "her hair was wild," he said.

She asked Zareff to help her get a more conservative look.

It was a delicate conversation. Addressing the topic of her hair, he told her this: "You know, I like it. It's great for the weekends or something, but you might want to do something calmer."

Executive presence is all about modifying surface-level characteristics, such as clothing style and speaking delivery, to help bring out a manager's inner character, Zareff said.

"It's all about the ability to command attention by the total package, being your authentic self," he said.

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