I use custom ringtones for groups. Anyone ringing with the default ringtone is immediately obvious as unknown, and I can easily decide to ignore/accept a caller

I use custom ringtones for groups. Anyone ringing with the default ringtone is immediately obvious as unknown, and I can easily decide to ignore/accept a caller. In practice, that means ignore. I should just drop a silent MP3 into my phone and use that as the default ringtone.