black triangle icon in menu bar
MacBookPro 15" w retina, late 2012
OS X 10.8.5 (ML)
Running either Safari or Numbers, with several other apps in the backgrouns, when I noticed a black equilateral triangle with rounded corners and no markings in the leftmost position of the 'icon' menus at the right end of the menu bar.
When I placed the mouse pointer on it, I got the spinning beachball, clicking it produced no action, so I launched Activity monitor to take a look at the process list, where there were no red text items saying 'such and such' is not responding.
I eventually did a restart and checked through all the accounts on the machine without seeing the icon again.
Any ideas as to what it was?
Rgards,
Barry
MacBook Pro with Retina display, OS X Mountain Lion (10.8.5)