Continuity mistake: While Sam considers going to see the psychiatrist professionally just to hook up with her, Carla suggests that he feign impotence, and Sam puts his bottle down on the counter, but it cuts to a closeup with Sam suddenly holding the bottle in his raised right hand. (00:09:30)
Continuity mistake: After dinner Sam pours Sheila a nightcap, and he opens a (seltzer?) bottle for himself. Sheila leaves, and both her semi-filled glass and Sam's bottle are on the counter. Just as Sam opens a second bottle for himself Rebecca enters, and Sam soon sets his second bottle down near his first. In following shots the amount of liquid in Sheila's glass increases, and Sam grabs his first bottle then walks away, but when Rebecca stands up, Sam's first bottle is back on the counter and it's his second bottle that's missing. (00:20:20)
Visible crew/equipment: After Sheila leaves the bar, when Sam hops up onto the counter Rebecca exits the office, and just as Sam says, "Hey, let me ask you something, do you think my life is empty and void of any meaning," the moving boom mic casts a shadow on the wall, over the office door. (00:20:35)
Plot hole: At closing time, Cliff, Norm and Woody spontaneously decide to go to Cliff's house. Sam then enters the bar after his date at Melville's. Later in the scene, Rebecca asks Sam about the 'Three Stooges', to which Sam sarcastically replies that they went to Cliff's house. But how could he possibly know that since he entered the scene after they had already left.
Continuity mistake: When Woody gives Norm a beer he puts a napkin next to the beer. The shot changes the napkin is under the beer.
Continuity mistake: During the scene when Norm is giving Doris the letter of recommendation her hair his covering her ear facing the camera. When she says "It must have taken a lot of guts to open up that way." Her hair is now behind her ear.
What is... Cliff Clavin? - S8-E14
Continuity mistake: At the point Cliff is disputing the fact that he thought his answer was right, on the right-hand side you can see the woman player's, Agnes, score. It says $400. Then in the next shot it changes to $3300. Then in a little bit later it changes back to $400. (00:14:30)
What is... Cliff Clavin? - S8-E14
Continuity mistake: Just before they reveal the answers of Final Jeopardy, they take a wide shot, and Cliff's question (Who are 3 people who have never been in my kitchen) is already revealed. But when they take a tight shot and ask Cliff to reveal his question, it is covered up.
Continuity mistake: After Frasier leaves to be bad, Norm starts talking. He puts his hands on the bar, the shot changes and he now has one hand on his glass of beer. (00:16:55)
Continuity mistake: When Cliff walks into the bar and walks over to Norm his beer is almost gone - the shot changes and it's full. (00:17:25)
Indoor Fun With Sammy and Robby - S8-E19
Continuity mistake: After Sam and Robin are done playing darts, Sam puts his darts on the pool table. The shot changes and the darts have moved.
The Ghost and Mrs. Lebec - S8-E23
Continuity mistake: When Carla is talking about seeing Eddie and the restaurant there is someone at the bar who puts their drink down. The shot changes, the drink has disappeared from the bar, and the person puts it down again.
Continuity mistake: Sam, Norm, and Woody are helping Rebecca move into Robin Colcord's house. When a curious Norm opens a bedroom door, the wall is bare. The shot cuts to Rebecca then back to Norm, but now there is a desk with flowers and a vase on it, plus a picture hanging on the wall.
Revealing mistake: When Rebecca is in the office and throws a drink on Sam, the pattern of wetness changes on Sams shirt.
Breaking in is Hard to Do - S9-E7
Continuity mistake: Rebecca walks to the bar, busily writing her love-letter to Robin on a notepad. As she speaks with Sam, she tilts the notepad toward the camera. We can see it is blank.
Continuity mistake: When Sam puts the paper from John on the bar it is next to a bowl, the next time we see it there is now more space between the bowl and the paper. Part of the paper is in the air, then the next shot when Sam picks up the paper it is lying flat on the bar.
Continuity mistake: In the scene where Sam talks to Henri, we can see Sam wearing a wedding ring. Of course, in the show, as a great lady's man, Sam is not married. (From 6:39 to 7:57).
Continuity mistake: The second time Frasier and Lilith come into the bar Sam is putting ice in glasses for them. Sam finishes the second one and puts it on the bar. The shot changes he is still putting ice in the second glass.
Get Your Kicks on Route 666 - S10-E2
Revealing mistake: When the guys are stranded you can tell the background is just a backdrop as the scene is not perfectly flat - there are some wrinkles in it. (00:13:05)
Get Your Kicks on Route 666 - S10-E2
Visible crew/equipment: The edge of the set can be seen after Norm drives up in the golf cart. (00:22:30)
Answer: Here is the source of the "WE WIN" photo: http://www.oldnycphotos.com/nyny587ac.html Brooklyn, of all places.