In reply to SARS:
Don't feed it, this can cause loads of problems. eg.
I have friends trying to control the weight of their cat but can't because she's a greedy thing and someone else is feeding her.
I have a friend who has pretty much lost a cat in a similar way. trying to control food intake, neighbour feeds cat, cat then decides to spend more time at neighbours, neighbour now claims ownership (until the cat needs vet services I'd bet).
Would you just randomly feed someone else's child because they wanted sweets but their parents had told them no?
If you have concerns contact the owner, if they aren't forthcoming call the RSPCA.