Continuity mistake: At the start of the movie when Cotton's girlfriend is being stalked by the killer, he stabs his knife through her bedroom door making a few large holes, especially with the first stab mark. Later, when Cotton finally gets to the house and is lookng for his girlfriend, he goes up to her door and there are now far smaller holes in the door, all in a nice pattern. When he smashes through the door, from the other side we can see there's no damage at all, then when his girlfriend emerges the stab marks are back, but in a different configuration. (00:07:35)
Answer: Not expressly, though it could have been the date of some significant event (December of 1988) but someone as security-conscious as Sydney now is wouldn't be stupid enough to have her code be something that could be guessed.