Usually there are tell-tale signs leading up to a redundancy. For a start most employees hear whispers that there is going to be a restructing of the company long before it is publicly announced. With your ear to the ground you may find out details, but it is enough to know that change is afoot. These changes may not directly impact you, but as soon as there are changes around you there must inevitably be some change in your role. Even if your job is safe you will be dealing with the loss of colleagues or the support of people in positions that are no longer filled.
You may start to feel like you are a marked person, no longer being trusted or given the responsibilities that you had come to expect. You may feel that your work is being looked at more carefully, or catch comments about your role that seem odd or out of place. In a big company you may notice people that you don't know walking around or attending meetings when there is no obvious explanation. Sometimes it is just plain old-fashioned gut instinct that things aren't as they should be.
Don't be paranoid about it, but it is probably time to find out just what your entitlements would be if your job suddenly disappeared.
You might also like to view Facing Redundancy: 8 Positive Steps to Take to help you prepare yourself personally or read my article Facing Redundancy: 8 things to do if you think your job might be made redundant.