Continuity mistake: When John's wife is in the bathroom she drinks all of the water in a cup, but when she throws it the cup is full again. (01:29:00)
Continuity mistake: When John Nash enters the cafe at the end and the people start giving him the pens, the first two go down pretty much perpendicular to him but later it shows them all turned 90 degrees. (02:04:25)
Continuity mistake: In one of the first scenes where Nash is being introduced to everyone around the punchbowl, the trees around them have CGI leaves added on since it was shot in January and had to look like early fall. In shots that show the trees' shadows on building walls, all we see is branches. Shouldn't there be leaves?
Continuity mistake: Near the end of the movie, when Prof. Nash goes back to Princeton, he is wearing a checkered brown and green shirt. The next day, he is wearing a light blue shirt, but when the scene changes, he is wearing the brown with green shirt again.
Continuity mistake: When the student approaches Prof. Nash in the Princeton library, he tells Prof. Nash he has been working on a mathematical theory. When the student hands Prof. Nash what appears to be a binder he does so by holding the binder with his left hand, palm down and fingers on top of the binder. In the immediately subsequent shot of both Prof. Nash and the student, Prof. Nash takes the binder from the student who is now holding the binder palm up, fingers under the binder.
Continuity mistake: When Alicia puts some pills on the table/desk for John Nash, the pills move/disappear/reappear, depending on which shot is used.
Continuity mistake: The second time Nash sees his old roommate's niece he drops his briefcase to hug her. A couple of shots later as he is walking away, his briefcase is back in his hands, without him having picked it up. Later in the film we see him from another man's point of view, and he is kneeling down, stroking the face of a girl who isn't there. He moves like he's really interacting with the imaginary people, so it can't be that he never really dropped his case.
Continuity mistake: During Nash's first lecture at Wheeler Labs, he writes a mathematical problem on the blackboard. However, you can see that the dimensions of spaces change between shots - first there is R^3, then R, and finally R^3 again.
Continuity mistake: During their first date, Nash and his date have a brief conversation where they have stopped walking after she makes the comment about God must be a painter. As the shot changes from each of their angles, the distance between the two changes each time. (01:04:10)
Continuity mistake: In the car chase at the dockside the car Nash is in screeches to a halt, veering slightly to the left. When they get out the car wheels are pointing to the right. (01:16:00)
Answer: You do not specify to which scene you are referring. The only window I recall with writing on it would be the window in Nash's room. John had covered this window in mathematical equations, theorems and geometric patterns. While most of the symbols used are Greek in origin, the language is simply that of mathematics.
Michael Albert