When I was in school the less well-off kids got their lunch free. There was definitely no equivalent to a "marker" the linked article mentions, unless you include the lunch ticket. I was actually kind of jealous at the time, I didn't understand why I had to pay when I didn't bring my own lunch and they didn't.
Singling out kids because their parents can't afford food is kind of fucked up.
It's been a while since I was in school, but my wife is a teacher here in the UK. The packed lunch area was often where the poor kids were, and we also had issues where (in their infinite wisdom) the school gave kids on free school meals a special card to get a specific meal (and nothing more). They may as well have stamped "bully me" on their foreheads.
Nowadays, schools are smart enough to use prepaid card systems where free school meals are preloaded on the same cards. My wife's old school used to put the same restrictions, but now it's far harder to determine who gets the free meals.
The packed lunch crowd does still get a lot of scrutiny, though, especially those that shop in "less favourable" stores. Buy your lunch from farmfoods and you're asking to be picked on. It's fucked up, and social media has made things SO much worse, but ultimately kids are often extremely cruel.