Creepiest marketing stunt ever? Staring people planted in crowds at baseball games across US

Baseball fans may have caught a glimpse of a creepy, smiling fan hanging out in the stands just behind home plate in the last week.

The bizarre fans were not actually just unshakeable fans of America's pastime — they were part of a viral marketing campaign for a new horror film called Smile.

Paramount Pictures sent the actors out to sit behind home plate at several games on Friday to stir up interest in the new movie, which is set to release in the US on 30 September and the UK on 28 September.

The movie follows a therapist as she investigates a claim that people have been dying after seeing an entity with an unsettling, rictus smile.

The actors appeared in the background of the Red Sox vs Yankees, Mets vs Athletics and Cardinals vs Dodgers games on Friday. All sat motionless in the stands and directed a sinister smile at the broadcast cameras throughout the game.

Baseball and movie fans noticed the bizarre incidents and shared images and video of the marketing stunt on Twitter.

"Here’s some fun, clever movie promo - Paramount seemingly placed #Smile actors in the crowd at both the Yankees and Mets games last night, both in view of cameras," Erik Davis, a film journalist, wrote. "The results were indeed creepy. Going to a game this weekend? Watch out for the smiles!"

A smiling actor also appeared beneath an umbrella in the background of the Today Show.

Viral marketing campaigns aren't terribly common, but stunts like Smile's aren't unheard of either.

In 2013, ahead of the Carrie remake, the production studio played a prank on patrons of a coffee shop when an actress in the store used "telekenetic" ability to throw another actor against a wall, and began making books and pictures fly from their spots, freaking out many of the customers in the store.

A year later to promote the film Devil's Due, an animatronic devil baby was carted around New York City in a stroller. It popped out and scared pedestrians, occasionally shooting milky "vomit" from its mouth.

Movies outside the horror genre have engaged in similar campaigns; in 2007, several 7-Eleven locations changed their signage into Kwik-E-Mart branding to promote The Simpsons Movie.

Perhaps the most memorable viral marketing campaign in film history was the promotion for the 1999 horror film The Blair Witch Project, which introduced audiences to the idea of a "found footage" movie at a time when the genre was relatively unheard of among the general public.

The movie presented itself in its marketing as a documentary, and missing posters featuring the actors were distributed at screenings of the film. A fake documentary, Curse of the Blair Witch, was aired on the SciFi Channel on 12 July, 1999 — just days before its wide release — to set the stage for the "local legend" of the eponymous witch. The fake documentary included witness interviews and was presented as truth.

The marketing was so convincing that many curious movie-goers at the turn of the century were convinced that a group of young adults really had gone missing in the woods after encountering some sinister force.