The "Trapitos" that were translated as "rag pickers" and "street urchins" if you allow Chrome to translate the article and common in popular spots at night.
I have never been to that town/neighborhood, but in other parts of Buenos Aires, "working class" people will stake out a street and wave a rag / white hand towel to get you to park in an open space "on their block".
They are not working for a parking lot company or waving people onto people's lawns like you see around Fair Park when going to the Texas/OU game. These guys are simply staking out free street parking and basically charging you to "watch your car". It is small time, but the exact same thing as the mob charging protection so that you store doesn't get burned down. (a.k.a. "extortion")
In this case, I think that they asked for US$10 and got US$8. (UPDATE: actually, slightly less than that)
In retrospect, I am thinking that they wish that they had paid the extra US$1.80.
I only was in a car when going out on the weekends when I was with my Argie girlfriend 15 years ago... but even then it was really annoying. She just had a subcompact Chevrolet 4 door at the time, so at least it didn't scream "This girl's loaded!" Other times it was walking, taxis, and buses.
People sometimes ask: "Do you miss Argentina?"
Answer: Some things I do, but trapitos are definitely not something I miss.