No show could possibly live up to this level of foreshadowing.
I had to disable the comments because every other comment was asking how something could have been a reference to Ford or telling me it was wrong and it got ANNOYING. So. Here is a list explaining every single one:
FORGOT: Vending Machine 1x1 : The vending machine that appears in the first episode leads down to the secret chamber where the machine that brings Ford back is kept.
FORGOT/DEBATED: Stanley Mobile 1x2 :
Stan's car has a license plate that says STNLYMBL which translates to Stanley Mobile. Dipper also points this out in Journal 3. I debated putting this one in because it refers to Stan's true identity and not Ford himself.
0:030:06 The Stan o' War 1x2 : As kids, Stan and Ford fix up a boat that they named "The Stan o' War". In the episode where Stan wants to take Dipper and Mabel fishing, he names his boat the same thing.
0:070:11 Wax Stan 1x3 : When Stan sees the wax figure that Mabel made of him, he freaks out because he thinks that Ford came back.
0:120:35 Wax Stan Funeral 1x3 : Stan holds a funeral for Wax Stan because Ford never got a funeral after disappearing because Stan took on his identity. Stan didn't know if his brother was even alive. He gets emotional because he misses his brother.
0:360:51 Ford 1x9 : The man who opens the door is not Stanley, but rather Ford himself. Note his glasses, sideburns, and chin.
0:521:02 Tax Fraud 1x14 : Stan is committing tax fraud because he files his taxes under the name of Stanford rather than Stanley.
1:031:22 Author 1x14 : Stan is referred to as an "author" while still going by Stanford. Before Ford's identity was revealed, he was exclusively referred to as "The Author".
1:231:28 Tax Fraud (again) 1x14 : More tax fraud shenanigans.
1:291:32 Ford's Glasses 1x16 : When Soos finds Ford's old room, Stan sees the pair of glasses that fell off Ford's face when he went through the portal on the nightstand. Stan spent many nights in this room on the couch staring at these glasses, wondering how to bring Ford back.
1:331:39 Ford's Glasses (again) 1x16 : Seeing Ford's glasses again brought back memories for Stan. He's sad. He misses his brother.
FORGOT: Image of Ford 1x19 : Gideon, not knowing his real name is Stanley because he's a fake psychic, refers to Stan as Stanford Pines, and images of the brand that gave Stan his "tattoo" (further talked about down the list) as well as Ford himself briefly appear on Bill.
1:401:53 Swing Set/Playground 1x19 : Growing up, Stan and Ford spent a lot of time on the beach's playground. They mostly spent their time on the swings. There was also a duck located next to the swing set. When Dipper, Mabel, and Soos enter Stan's mind, we see a recreation of that playground. The swing that Stan would sit on is broken, because his relationship with Ford is broken and he feels guilty, especially since Ford has been gone for such a long time and he was never able to apologize for screwing up.
1:542:02 Boxing Lessons 1x19 : In the background, we see a child reading a book. As a result, we cannot see his face, but we can see that he has the same haircut as Stanley. This child is Ford.
2:032:10 Portal Blueprints 1x20 : Dipper flips to the pages in the journal that are part of the blueprint to the machine that brings Ford back.
2:112:49 The Machine 1x20 : Now that Stan has all three journals, he has all the information he needs in order to bring Ford back.
2:503:02 Stan's Secret Tattoo Gravity Falls Short : Stan's "tattoo" is not a tattoo at all. It is a brand mark, caused by the fight he and Ford broke out into the night Ford went into the portal.
3:033:15 Glove 2x1 : While working on the machine, Stan puts on a rubber glove that contains six fingers. This belonged to and was likely made by Ford himself.
3:163:27 Shapeshifter 2x2 : The shapeshifter states that the author hasn't been "himself" in thirty years. Stan has been using Ford's identity for thirty years. The author isn't "himself" at all. He's Stan.
3:283:57 Fiddleford 2x7 : McGucket speaks of Ford in his Blind Eye confession, as well as the machine that took Ford away from his dimension. There is also a drawing of it in the background.
3:584:05 Stan's Monologue 2x7 : Stanley is desperate to bring his brother back. The picture focusing on the twins foreshadows him bringing back his own twin.
4:064:15 Poindexter 2x11 : When reading in the journal, Stan refers to the Author as "Poindexter". This was a nickname for Ford growing up.
ALSO: Dunno if this counts, but in the first episode Stan was wearing a mask that was kept in his and Ford's room.
Disclaimer: Gravity Falls is owned by Disney and Alex Hirsch.
Credit:
1. • gf clips for videos
2. • Video
3. • Playlist