Nobody likes getting fired, and the truth is, most managers don't like firing people. Sometimes, just to avoid the unpleasantness of letting an employee go, the boss will slowly indicate that you're presence is no longer needed. Whether he does this directly or indirectly, once you get the hint that you're on the chopping block, it's time to start looking for a new job.
You're No Longer in the Loop
A big sign that you're about to get fired is when you are no longer privy to information you used to be. This may not necessarily be at the direction of the boss, but based on the talk around the office, prompting everyone to treat you as though you already no longer work there. If people below your position are getting information before you, it may be a sign the boss is about to fire you or get you to quit.
People Avoid You
If the word is out around the office that you are no longer welcome, your co-workers may find it difficult to interact with you. If people who used to talk to you -- even just small talk -- are now ignoring you, you might be on the track to unemployment. This may be a result if your performance is lackluster, causing people to stay far away; or, your boss may be sending you a message by telling everyone -- except you, of course -- that he wants you out.
If you've been stripped of your responsibilities, there's definitely something foul going on. No longer having the responsibilities you used to have shows that you're not actually needed in the company. This makes it easier to lose you as an employee, as you won't leave a hole in the company's workload. Making him feel of little or no value to the company is one way to get an employee thinking about moving on to opportunities elsewhere.
Forced Time Off
If your boss asks you to take some time off work, your future at the company is grim at best. Unless the boss gives you time off for a job well done, then he's probably evaluating how much the company really needs you. If you in a job in which you are paid by the hour, making you take time off may also be a way of cutting back your hours enough to where you feel you have to quit and find a new job just to stay financially stable.