After Sarah plants the gun in Tony's right hand she goes into the bathroom to clean up. When she comes out and kneels by Tony, the gun is no longer there.
In the last scene where Tony and Sarah made love, it shows his left hand, and there is a ring on his wedding finger. Later on in the movie, he has two rings on, one still on his wedding finger.
In one of the last scenes (1:22:30) Tony points a Beretta M9 at Susan, but when the shot changes from the front to side/back of Tony pointing the gun at her. On the front facing shots with the gun, the gun is in "Loaded Closed Receiver" form, but in the side/back shots the gun is in an "Empty Open Receiver" form.