This is common in Brazil and I suspect that's where it comes from. Haven't seen it happening much in other parts of Argentina outside of BsAs.
It drove me nuts in Brazil how everyone from Bus drivers to store clerks would hiss to get your attention or someone elses. It's not so much a hiss as a pssst kind of sound. You only do it if someone isn't looking at you by the way, as I found out. I psssted at one guy while looking at him and he seemed insulted.
I have seen this strange habit a lot in the Hippodromo in Palermo which to me brings out the worst in people . 1000s of people cramped in a fantasy world with the poker machines flashing becokoning crazed hyped up people to depart with their pesos.