Secret message perhaps like our local FOX affiliate does with 'EAT'?
Or possibly more seriously, it may be a prelude to using that sorta like a sidebar ala Vista style, where they can show scrolling news tickers and weather data whether it's in a commercial or not? both our WTVW (FOX) and WFIE (NBC) have their tickers on the bottom 1/4 of the screen whether or not they're in a commercial break so it may be some sort of future thing very similar.