COEUR d'ALENE — Smoke billowing from the boys bathroom as rebellious teens lit up cigarettes during school more than likely got the teens immortalized — and in trouble.

But what happens when the tell-tale signs of tobacco use like odors and smoke aren't there?

With the rise in popularity of electronic cigarette use among youth, that’s a real challenge for school administrators.

"They're easily disguised. Many look like pens and hide easily in backpacks," said Coeur d'Alene High School Assistant Principal Libbi Keyes. "And they're easily accessible — I've even had a few teens who secured their e-cigarette from their parent's drawer at home."

On Thursday, the office of U.S. Surgeon General Vivek Murthy issued its first report on the use of e-cigarettes among youth and young adults. E-cigarettes — which go by many other names, but are generally defined as an implement that delivers nicotine, flavoring, and other additives to users via an inhaled aerosol — are now the most commonly used form of tobacco among youth in the United States. According to the report, use of the devices by high-school students has grown by 900 percent from 2011 to 2015.

"Although we continue to learn more about e-cigarettes with each passing day, we currently know enough to take action to protect our nation's young people from being harmed by these products," Dr. Murthy wrote in the report.

Post Falls Police Capt. Greg McLean, who works as a school resource officer, said law enforcement officers are encountering more and more youths with electronic cigarettes. McLean said the rumor mill often swirls about a student with one of the devices at school, leading to confiscated e-cigs and parents being notified.

As the e-cigarette market continues to grow — projected sales of devices and accessories was $3.5 billion in 2015 — the surgeon general's report states companies selling the products are beginning to share many of the marketing techniques commonly used by the tobacco industry. These marketing efforts, according to the report, reach a "wide variety of channels that have broad reach among youth and young adults."

"I feel like the marketing makes it more appealing to teens," McLean said. "Maybe the kid doesn't like the taste of cigarettes, but if they can get it in, like, a bubble gum flavor, it doesn't feel or taste like a cigarette anymore."

Dr. Murthy recommended efforts to regulate, to the extent allowed by law, the marketing of e-cigarettes to youth. The city of Coeur d'Alene, according to Deputy City Administrator Sam Taylor, was ahead of its time and passed an ordinance in 2011 that, in addition to clarifying products that should not be sold to minors, made it a violation to market e-cigarette products in a way that would appear appealing to those under the age of 18.

McLean told The Press the city of Post Falls also enacted a similar ordinance in 2011.

In addition to the marketing regulations, the report also recommends retail licensure be a requirement for those who sell e-cigarette products, as well as "significant increases in tax and price." Finally, the report states that education efforts targeting youths are needed to reduce the number of underage users.

"I don't think they look at them as a cigarette," McLean said while stressing the need for constant education efforts. "When you look at the compounds in the liquid though, it's the same."

At Coeur d'Alene High School, Keyes said education is the key to solving the problem of e-cigarette use by minors. The school, she added, offers tobacco cessation classes to reiterate to students that, although the devices look different than traditional tobacco products, they still can have lasting and harmful effects.

"If our young people are aware of the harmful effects, they may make healthy choices," Keyes said.