Couple of things:
First, I read your previous question and I'm not convinced it is an antenna fault. However, to answer your question the antenna looks like this and costs about $2.00.
Second, I believe, if it is a hardware issue, that it may be the SIM card reader itself. If that is the case you may need a new logic board.
Third, the little "x" in the signal area usually means that it is still actively searching for a signal, but is not in range of one. So it is possible that since you were changing settings for unlocking the phone that it is searching for a signal that is is out of range of. If this is the case it means your hardware is all perfectly fine and you have a software (settings) issue.