A big part of the film is the clock tower, the lightning that strikes it, and the way Marty and the past-version of Doc Brown use it to send Marty back to his own time.
Marty gets a pamphlet in ’85 that tells him everything he knows about when the lightning will strike, urging him to help save the clock tower from destruction. The irony is that Marty and Doc Brown were the reason the clock tower was struck by lightning in the first place since they attach a lightning rod to attract the lightning bolt.
Set to be President
On the wall of Hill Valley High School in 1955, there's a sign that appears on the wall that is begging you to vote for Ron Woodward for senior class president.
It turns out Ron Woodward was the name of a key grip, in charge of rigging and lighting for the movie, and the set decorators used his name on the poster as a joke. After standing up to Biff Tannen, George McFly wonders if he should run for class president, which means he might have tried to go up against Woodward.
Zemeckis Self-References
The town of Hill Valley is a place of many references, and though this one might be a coincidence, we could one hundred percent believe that it was intentional.
In the scene where Marty hitches a ride on the back of a pick-up truck on his skateboard, he passes a “Used Cars” sign. It's nothing out of the ordinary, but “Used Cars” is actually the title of the first film that Robert Zemeckis and Bob Gale collaborated on, a satirical black comedy released in 1980.
More Foreshadowing
When Marty lands in 1955 and has dinner with his mother's family, they're watching an episode of "The Honeymooners". Marty calls the episode a classic, surprising everyone – mostly since it was the first time the episode aired, and it was even the very first episode of the show.
Looking closely at the television has actor Jackie Gleason dressed as an alien, which foreshadows a trick Marty pulls on his father a little bit later in the movie. It was the only way Marty was able to convince his father to ask Lorraine out, which sets much of the plot in motion.
Follow the Yellow Brick Road
When Marty drives the DeLorean through time to thirty years in the past, he goes from an empty mall parking lot to the middle of a farmer's field. The very first thing he sees after the night sky and trees is a scarecrow in the middle of the field.
While it's pretty common to see a scarecrow in a field, it's been thought this is a subtle reference to "The Wizard of Oz". Everybody remembers the Scarecrow on his search for a brain, but it's one of the first main characters that Dorothy meets when she lands in the strange land of Oz.