Continuity mistake: During the scene when Sam and Diane are left alone in the cockpit, the position of the curtain behind them keeps changing. When Sam is speaking, the curtain is half open. When the camera angle switches to Diane, the curtain is closed.
Other mistake: After Andy leaves with his girlfriend, Diane goes to call the cops. Problem is that when she lifts the phone onto the bar, there's no cord connecting it to the phone jack.
Continuity mistake: Diane's outfit (shirt/sweater) changes in the scene where Sam is lighting candles. (00:07:18)
Fools and Their Money - S4-E12
Continuity mistake: When Sam asks Woody to go into the office to talk privately, Woody has no apron on. As they walk in to the office, Woody has the apron on, which then disappears.
Continuity mistake: In the back room, Norm's glass goes from nearly empty to half full and back.
The Peterson Principle - S4-E18
Continuity mistake: When Norm says "you're right, guys don't tell on other guys" the cigar he is holding suddenly moves to the beer mug in front of him.
Continuity mistake: When Sam goes over to talk to the guy sitting at the table, the door opens and someone walks in, the shot changes and the person has disappeared.
Visible crew/equipment: In the opening scene after Sam says "I think this calls for drastic measures" there is a shadow of the camera on the wall behind Norm.
Visible crew/equipment: When Cliff's father comes into the bar for the first time and is standing by the bar, the end of the set the brick wall changes to a curtain. (00:07:45)
Visible crew/equipment: When Norm walks in at the beginning of the episode you can see the end of the set the brick wall changes to a curtain.
Visible crew/equipment: When Carla says "You're kidding" about the picture she has, a boom mic is visible. (00:12:20)
Birth, Death, Love and Rice - S4-E1
Continuity mistake: Sam puts a empty champagne glass in front of Norm, the shot changes and the glass is now full.
Visible crew/equipment: At the end of the episode when Cliff is talking you can see the end of the set, the brick wall changes to a curtain. (00:23:55)
Continuity mistake: When Claudia is saying goodbye to Sam she is holding her purse and a magazine, at first the purse is against her body, the shot changes and the magazine is.
Birth, Death, Love and Rice - S4-E1
Continuity mistake: When Cliff and Norm are walking from the pool room there is a beer on the counter. The shot changes and it disappears. Norm sits down and it reappears, only to disappear when the shot changes.
Answer: Here is the source of the "WE WIN" photo: http://www.oldnycphotos.com/nyny587ac.html Brooklyn, of all places.