glosshog,
An additional thought, for what it's worth...
You may have seen a pointer to an application or item which at one time was added, perhaps inadvertently, to your Finder toolbar. At some later point the item was deleted and thereafter the pointer had nothing to point to because the original could not be found.
The condition is easily reproducible. Choose an item on your hard drive -- a text file, image, small 3rd-party utility, AppleScript, e.g. -- and
duplicate it. Open a Finder window and drag the
duplicate item to the Finder toolbar (it might take a bit of coaxing for the item to find a position where it will stick; look for the green "+" sign). Once added, find the
duplicate item you just created and send it to the Trash. And then empty the Trash. Open a new Finder window and you should see a question mark identical to the one seen in your screen shot. To remove the question mark -- or any toolbar item for that matter -- click and hold on the item with the command key pressed down, and drag the item from the toolbar until you see it go "poof."
Regards, Andrew99