Just received JellyBean 4.1.2 on my Sprint Samsung Galaxy S3. I have always used the 4x2 digital clock widget and I noticed a small icon that looks like a clock appearing just above the AM/PM. This also appears when displaying the weather for the various cities. What does it mean?
Going by your description, you're referring to the object circled in this screenshot
That thing indicates that the city the time is being shown for is currently running on daylight savings time. In this screenshot, we see that New York is observing daylight savings time, and Phoenix isn't.