The top 10 warning signs that you are about to be fired would definitely start in my opinion when they start not acknowledging you. And by that I mean they do not acknowledge you in the office or workplace, and therefore they are not required to acknowledge any accomplishments of yours. This in turn puts you on the outside of the equation and diminishes any worth you have towards the company. It's much easier to fire someone that has become steadily worthless to the cause tan someone that is constantly involved int he decision making.
The second warning sign that occurs is concerning any off time requested will be denied, even for valid reasons. If, for instance you became sick and had to call in they would require a doctors excuse before you could return to work, even if the illness was a virus or 24 hour bug.
The third sign that I believe occurs is when beginning new projects they select someone else even though the other person does not have the qualifications that you have.
The fourth sign I believe occurs is that they cut your scheduled work hours thus reducing the total compensation that you would otherwise receive.
The fifth sign that occurs is when they know there are specific times that you cannot work for instance a person that has obligations and has never worked a specific day due to the fact that they might recieve visitation with thier children from a previous marriage. Once they schedule that person into work when they know that they cannot work it that also shows a telltale sign that the person is on the way to being fired!
The sixth sign that occurs is that they start picking over your work looking for mistakes. They may nag or badger you wanting things done a specific way even though that way is not economical or precise.
The seventh sign that you are about to be fired is that they start questioning your motive on every single job you perform, and refrain from asking you to do anything other than grudging tasks that are not work specific to your position.
The eighth sign that they are about to fire you is they start putting someone to oversee or second guess your work. as if they are unable to trust your judgement.
The ninth sign that you are about to be fired is they start writing you up for every little infraction when someone else who has the same infraction is allowed to go without any type of discipline or acknowledgment.
The tenth sign you are about to be fired is when you have a badge for security reasons and it no longer opens the door to allow you to have access to the building issue.