Need to file a return for 2 yrs prior to dad's death. Do we put "died in 2016" in signature line and file as joint, since he was alive then?

Dad passed in 2016.  We have filed the joint return with my mom for that year and reported that he passed away.  But now find out that we need to file a 2015 return.  How do we do that?  Assume we will file joint as he was alive then, but put "deceased 2016" in the signature line?