In Quicktime, such a bar is a text track, usually used for subtitles or chapter markers or things like this. If you have QT Pro and you open the footage in it, then check the properties you'll see a text track has been added to the video track and audio track. You can delete it safely from there.
If you have any chapter markers which you want to take forwards to DVDSP then these will be lost. The bar tends to appear when markers are placed using alternative NLEs instead of FCP, although I have managed to set markers badly in FCP before now and get the bar from there, too.