On some things, scratches and scuff marks just add to the item's character. Many antiques lose value if you polish them.
The only way to remove a scratch in bare aluminium is to buff around it down to the scratch. Alternatively, you could give it a wire-brushed or sandblasted finish - which the scratch could be camouflaged in if you do it right.
If it is anodized black then you could blacken it with a marker pen ... or with chemicals such as Birchwood Casey Aluminum Black (gun store), but the latter is a bit expensive for just a tiny scratch.
But if your case is anodized in a colour, then you are out of luck.
