Dear some cars have "P R N D S L" or "P R N D3 D2 L" whereas alto comes with "P R N D L" when you press the "S" button on the side of gear stick it only applies to "D" and runs it on low gears. You can obviously turn it off by pressing it again
for the second part yes it shows a letter "S" in the dash even in parking, because when you press "S" Eco and idling mode cannot be engaged (means S in parking is for your info only)