For non-Covid reasons, my family left NYC in mid-June and we plan to return mid-August. The State we're in recently made it onto NY State's quarantine list. I fully intend to quarantine when I return, but I'm still concerned neighbors will "turn me in" when they see me in late-August. I can understand that when they see me for the first time in months, they won't know I've been hiding away in my apartment for 14 days. Is it odd to try and announce to people, "hey, I've been quarantined! Don't report me!"

Post on social media that you are back and locking yourself in. Ask doorman to have your mail/packages brought upstairs. Our building was very helpful when people had to quarantine during the height of this, I'd assume they'd want to be as helpful as possible to keep numbers down. Obviously tip staff or make arrangements to do so.
How do you get food/medicine/personal items if you’re quarantining ? Does a public worker bring it to you? Not everything can be delivered.
And finally, if you have actually quarantined for the full two weeks, and someone tries to confront you, simply say so, citing the date you returned. Presumably, if officials became involved ( which is highly unlikely), and you do not have a doorman or super who can confirm, your cell phone records would provide sufficient corroboration.
This is a very odd question. If you ACTUALLY quarantine, that means none of you will leave your apartment for two weeks. So nobody will see you, either in your building or especially out in the neighborhood, and there won’t be anything to report. Right?
Just tell people you’ve been in upstate NY.
Just tell everyone you’ve been in upstate NY.
Note that New York City is checking your phone records; I received a couple of reminders from the City when I returned from Florida.
Update that I just saw that NY State has a mandatory self-registry. So I guess if I just register when I get back, then I'm already on a list, and I don't have to worry about getting reported.
Why do you think people in NYC are reporting people? I think you're being a bit paranoid. No one I know has reported anyone. If they know someone has just come back in from another state, they do not socialize with them. I mean, we're really only doing socially distanced socializing outside. But I had a friend who had to go on a work trip a month ago. He came back and shut it down for 2 weeks. Totally normal.
What did you do to piss off your neighbors? lol.
apartment or house?