Cutty 12 to be precise. One thing that consistently impresses me about AMC's Mad Men is the attention to detail. Everything from fashion to slang to cigarettes and especially alcohol is historically accurate. In this scene from season 7 episode 2, Peter Campbell (Vincent Kartheiser) drinks from a vintage bottle of Cutty 12.
I'm not sure exactly when they changed the label from simply "Cutty 12" to "Cutty Sark 12 year" but I'm pretty sure it was around the late 70s or early 80s. Either way, I'd pay top dollar for this retro bottle today.