If you're checking out a playlist of modern hip-hop videos, it's not going to be long before you spot a product placement for a vape pen. Many rappers have partnered up with marijuana tech startups, so it's no surprise that those companies' products are showing up in their videos. Snoop Dogg and Wiz Khalifa both have endorsement deals with Grenco Science, The Weeknd did a collab with PAX, and KandyPen products have popped up in videos from Fetty Wap, Migos, and Kid Ink.

Product placements have been standard practice in music videos for decades, but there is a legal reason behind the explosion of celebrity endorsements for marijuana companies. Most states, even ones where pot is totally legal, prohibit all other forms of advertising for marijuana. In California, Prop 64 prohibits all advertising via broadcast, cable, radio, print, or the internet unless "at least 71.6 percent of the audience is reasonably expected to be 21 years of age or older."

Colorado has a similar law limiting advertising to outlets where 70% of the audience is over 21. The state also outlaws pot-related pop-up ads as well as ads targeted at “out of states persons.” Online, Google and Facebook both prohibit the advertising of marijuana-related products. With all of these restrictions, celebrity endorsements are one of the only ways for canna-businesses to advertise their products.

Many new startups have sprung up to address the advertising needs of the legal weed industry, including Green Street, a cannabis creative agency that has brokered deals with A-list rappers as well as representing major global weed festivals.

"I think it's the same no matter what the product is, whether it's cannabis or not," said Green Street president Rama Mayo. "The kids know what's up. They know if you're getting paid to sell something or if you really love it. It's our goal to find artists and brands who really love each other. You want to find someone who actually uses the product, whose friends use the product, who's down with the community."

Celebrity endorsements and product placements “just work,” according to Roger van Zandt, VP of Sales for KandyPens. "We have 12 celebrity endorsements. We've done over 35 videos, product integrations. We're carried by the biggest distributors in the nation, and so we're in all major storefronts, so when someone is in the market for a vaporizer, we hope that they'll choose ours because of all the different places that they've seen it."