Would you sign this agreement?

The employment agreement I received says something to the effect of " employee will have a 12 week probationary period where she is expected to complete the goals outlined by employer," but it doesn't state what the goals are.  HR said that the goals will be set when I start.  I asked that they just change it to say that I have a 12 week probationary period if they can't spell out what the goals are in the agreement.  I think a 90 day probationary period is pretty standard and it is at-will employment, so they could fire me for anything at any time.  I'm not sure why this part about meeting goals is in there and I'm not sure if it is really important, but I do know that I don't feel like agreeing to something that isn't specified.