You don’t see it as much these days, but YC portfolio companies can post privileged threads on this site for job listings, which in practice double as ads for the company. You’re not allowed to comment on them.
I haven’t seen one for a while because I suspect every company is already inundated with 1000 applications for every job in this market, but this is what Hacker News was for.
Y Combinator is right there in the URL. People know and don't care because it's a well run forum with interesting discussions, the privileged posts don't change that.
Most people aren't so slavishly devoted to capital that they have memorized the names of firms.
But, it is social media. Just that they make a point to try and tone it down and keep it focused.