The mystery is solved(!)
Remember this?
I blogged about it ages ago, and everyone wondered what it was. It turns out that two people were correct; it was both a "doorstop" (according to S) and a "thing to stop doors slamming on fingers" (according to iks).
And I know this how? Because I found evidence the other day, which doubled as evidence that having a camera on your new mobile phone is actually useful sometimes:
The bad news? I've lost it, so cannot stop my doors slamming on my fingers. Oh, never mind.