Are you an Aboriginal or Torres Strait reader? if not, then the warning doesn't apply for you and you can go about your day, or you can do two seconds research and find out why, if you're curious.

Others have already answered, but I will add that it varies from tribe to tribe, but also includes that it's not just out of respect, but some tribes believe if you mention a deceased persons name too much or show their voice or image, they will not be able to properly rest, and it may call someone back from the dead, and that's how you get ghosts and unquiet spirits. Yes, not everybody literally believes that in modern times, but they still follow it out of respect. For some tribes though, this ban expires after a certain period of time (like a month or a year), others it does not. Other times family may waive this ban, especially if they were a prominent person, like a singer or political figure. But yeah, I have relatives who are only referred to by their relationship to others (e.g. his grandmother, their aunty) and not their actual name.