Plus / Minus sign is constantly blinking on Nikon D300 camera?

I noticed that the +/- (plus / minus) icon keeps blinking on my Nikon D300. I don't remember when and why it started but for a long time, no matter what I do (I played with settings, changed ISO, mods, etc. ) it keeps blinking at all times.
Besides that everything seems to be normal.
What is wrong?

Are you shooting in the dark? Take note that low light to you may already be total darkness to the camera.

Have you done your homework and bothered to crack the owner's manual? Details are most likely there.

When you press the +/- does the display show 0.0? If not rotate the main (or maybe front depending on how your camera is set up) dial til it reads back to 0.0
is it the flash compensation or exposure compensation +/-? You'll have 2 options, try them both.
you didn't say what exposure/shooting mode your camera is in, which may have something to do with it.

I've played with my D700 and I can't get the +/- to blink.