'S' is commonly used at the end of a message to represent sex. Similar to 'X' in the UK (kisses) and 'Xs and Os' (kisses and hugs) in North America, 'S' could be used between two people of the same sex without being regarded as homosexual. Usually more Ss means more intense sexual tension between the two parties.
Long time since we've chilled. I heard you are joining us in Montreal!! It's going to be EPIC!