A couple weeks ago someone was sending Hello Nostr from new empty accounts every second, so global feed was useless. Every message contained some POW even. It wasn't really malicious though - it didn't try to send to every single relay, didn't change the content, and didn't send 100x as much. So a couple relays were banned by clients, and "Hello Nostr :)" was blacklisted, and then the spammer turned it off.
Then there was a guy who was thrashing another one by answering to random threads from several accounts, and no one had any good idea of how to fight that.
The only reason you don't see that every single day is because no one is doing it atm. It's just a question of time until nostr annoys someone and it comes back.
I remember the Hello Nostr thing that people were talking about but I didn't happen to see any. But it also might have been a very busy week for me offline.
I was hoping to subscribe to a service like you might do with a pihole that blocks ads, or an email provider that blocks spam. One that maintains a good reputation for being limited in their scope, who doesn't block political content they disagree with. Should such a service arise and suggest a protocol, I'll plug gossip into it.
you have notes that are moderation actions and you subscribe to them, and you can subscribe to pools of these from many users