I am going out on short term disability (paid) soon , an operation, est 8 weeks. Should I sign up for FMLA to ensure I have a job when I return?

The answer to your question depends on whether you trust your employer or not.  Technically, you would be protected for your 8 weeks under the FMLA.  And if the employer has so chose, it could be counting the 8 week period against your FMLA allotted 12 weeks even if you do not specifically request FMLA, provided that they tell you they are counting this time against your FMLA.  It is possible, however, though certainly not a guarantee, that if neither you nor your employer refer to this 8 weeks as being under the FMLA, then should need additional time after your surgery to be off work due to complications, then you might possibly have that 12 weeks of FMLA still in the bank, so to speak, to cover you for another medical absence if needed.  This not a guarantee, however, as there are some court cases that would not allow you to get this added benefit. Contact an attorney in your area to review all your facts before deciding.  Seeking FMLA is the safer bet, especially if the 8 week period should be plenty of time to recover and the risk of complications is unlikely.