Haven't heard the immigration question, but that is a quite logical one. Smart FA on that plane!
I have had the "Welcome back!", the less polished "Oh, you are back?!" and the witty "I will try not to forget your coat this time!" (I had to the remind staff about my jacket on deplaning) but I guess it is easier to remember a face and say something witty/smart when pax in 1A returns.
As for the "signing paper" question, how about we all start responding "Yeah, I'm legally divorced now! How about we celebrate that tonight?"