Some people that come to our house do not press our ring doorbell and simply knock the door instead (no knocker so just tapping on the door). The ring doorbell is hard to miss.
I think they do it as they think they won’t be on camera if they don’t press the bell (it records from 1m away so we know they’re there before they even knock!)
Next time I'm planning to wait and let them knock again so i can point out the bell and say we don’t really hear it when people just knock.