Has two meanings for two different sites.
Support for Support
Its pretty much advertising someone else but its done through bulletins. normally people
do s4s for Layout sites, Bands
on YouTube s4s means
Subscribe for Subscription
You subscribe to someone because they subscribed to you.
Band: "hey we really need more
friends can you help
us get more
Girl: "sure but only s4s"
Band: "ok cool we posted a bulletin telling
all our friends to add you, please return the favor"
-1 min. later-
Girl: "awesome I posted a bulletin to all my friends telling
them to add you!"
In return both users receive a benefit.
Guy1: "hey everyone
Guy2: "cool, i subbed you. now subscribe back! :)"
Guy1: "thanks dude and yes i subbed back"
Both Users receive a subscription.