1999 528i - Can anyone tell me what the heck that little black triangle thing is on the back area above and behind the back seats (where the speakers are) just before you hit the rear windshield? It's not even centered, it's off to the left (looking back from the front)... no clue!

I called my local BMW service today and the Manager couldn't even tell me, he said "bring it in, and we'll take a look at it for you"...

I just can't get there anytime soon and thought I'd ask here. I've been wondering forever what it is!?!

Thanks for any help you can give me!

For holding the center seat belt when not in use.