Do you mean the drop-down list that shows up when you right-click on the signature (in the Signature Panel or signature field)?
I do not think that just saving a PDF with no changes would result in that unless you somehow flattened the PDF.
Can you see the signature in the Signature Panel? Can you expand ([+] at left) the signature? Does the Signature Panel provide info for this signature? Is the signature validated? If "yes" then is the signature status Valid?
It could be that when you saved the file you somehow flattened the signature, so that now you have only signature appearance in the PDF but not a real signature field which contains all signature properties. If the Signature Panel does not contain your signature (enpty if your signature was the only one) then this is the most likely cause.