I would only seal the tiles if the manufacturer advises it. Glass and ceramics don't need it, most porcelain don't usually need it just more porous types of natural stone.
Hope that helps.
Hi mate,
B+Q and topps tiles do a specialist natural stone cleaner which might help though silicon is difficult to remove, of the two i would try Topps'.
You might want to have a go with solvent cleaner which you can get from your local hardware store.