What is the recommended way to flag a contact as being deceased in the Contacts app on Lion or Mountain Lion? Death is a sad fact of life and over the years some of my old contacts have died.  I still wish to keep a record of their details, birthday, day they died, notes, spouse, kids etc in my Contacts and am looking for a recommended way to flag those records to indicate that the person is dead. I am interested to know how other people have dealt with this.
I've had the same "need." I guess we all do sooner or later. Here's what I did.

Card menu > Add Field > Dates. Then select the Date field drop down in the contact and select custom.

You can also change the general new contact template in the same Cart menu.

I hope this helps.