6. "Observers Are Here" - Fringe
Fringe creator J. J. Abrams is a lover of the mystery box, so it's little surprise that his penchant for sneaky trickery extends to the show's visually striking title sequence.
Now, this one is really tough to spot. Just after the words "dark matter" appear on the screen, there is a momentary flash of light, and if you scan through the following frames at low-speed, you'll find that there's a single frame containing the hand-written words, "observers are here."
The Observers are of course the show's shadowy antagonists, and so right from the show's very first episode, Abrams is subliminally warning the audience to be wary of them.
There's virtually no chance of catching the Easter egg when viewed at full speed, so you're better off slowing the below clip down to 0.25x and keeping your eyes super-peeled at the 0:16 mark.