Recently, I've been noticing a small arrow in "Messages" and my email folder, only when I turn on my berry. After I scroll down using the trackball, it goes away, until next time I turn on my phone. See the attached image to see what I mean.
Yeah it does appear to be a scroll down arrow. Odd that it's there with an empty messages folder as shown in the pic though. Some strange glitch, might try switching themes if you're using a 3rd party one at this time and see if it goes away.