No idea what it is, but it does not look used, so possibly something mislaid in the car when built, and all owners have just kept it, 'just in case'. If it has not been fitted to the car since 2003, there's probably no need to worry.
There's probably an identical bracket fitted in the correct location, your mission, if you choose to accept it, is to find it and report back with a smug smile.
Edit: Just thought - folding seat hinge bracket?