It may be absolutely nothing, but rewatching Two Cities for the 3rd time, I realized that when they show Jack in the car keeping tabs on Sarah, the radio is playing a song by Glenn Miller which I recognize but don't know the name of offhand.

I do, however, know that the last time I heard that song was when Sayid and Hurley tuned in that garbled radio signal on the Island last season. They commented that they didn't know where it came from, and Hurley added cryptically "Or when..." or something to that effect. At the time it made me think time warp, but I don't think that is the case in this instance.

Jack saw his dad's ghost on the Island, heard his dad's voice over the speaker in the Hydra station, and a song that meant something to a specific time and place in his life was broadcasting on a radio carrier on an Island in the middle of nowhere.

Or maybe Lost just can't afford a lot of music licenses...