I bought a new (ceramic) soap dispenser a couple of weeks back and now there's a watermark on my porcelain sink where I used to keep it (picture below with increased contrast). First off, I don't think it's a hard-water stain. There's always a layer of water between the soap dispenser and the sink. I think this water caused the stain (it smelled very bad too -- like ammonia and rotten eggs). Any ideas on how to remove the stain?
EDIT: After some investigation it seems that such stains are caused due the porcelain absorbing water. This is more common with granite counters and to prevent further staining, the granite has to be "resealed".