Top signs that your company is about to have layoffs.
They discontinue the free soda and juice.
They request a copy of everyone's resume to "update their files."
You get an email of any sort from the CEO or the President of the company (provided that person is not your immediate boss), particularly if it mentions how the company is doing. Positive messages about how the company is doing may be worse than cautious ones.
There is a sudden push for cross training, particularly when your company hasn't stressed it before.
Provided you are in the same building as upper management, you notice that ALL of them are gone for over two weeks on a "retreat," and it's not the week of Christmas or July 4th.
The company lowers their percentage of 401k contributions, or moves out the time it takes to vest. If they stop the 401k entirely, expect it within days.
You merge with another company (and don't assume you're safe if it was your company that bought another).
A large percentage of upper management leaves the company for "other opportunities."
There is a company-wide email about using printers and copiers for personal use. (They don't want to lose all that paper and toner on resumes and cover letters.)
You read about a big lawsuit against your company in the paper, particularly if that lawsuit is not mentioned via any internal communication.
Top signs that YOU are about to be laid off.
People cast pained looks at you during meetings, and you didn't even fart or anything.
Someone you don't know shows up and pretends to talk to you, but you notice they are really scoping out your cube/office.
You are suddenly not on mass emails you've always been on, or are no longer invited to meetings that you used to attend.
You notice any HR person noticing you. (Meaning, any glance at you that is more potent or significant than the kind of glance a farmer gives to his cows is bad.)
Hall conversations stop when you approach.
Someone inquires as to what kind of computer you have, and how powerful it is, how big the hard drive, etc. Especially if you have a laptop.
Your manager stops by and wants a written summary of everything you're working on.
People stop laughing at Office Space jokes.
The secretaries/executive assistants start treating you with more disdain than usual. Or, if they've always been very disdainful, they suddenly get very nice.