Can’t claim this is a best practice, but what we’ve done is:
- Create a pinned topic that covers the subject, explains the value of having updated profiles, and explains how to update the fields we care about.
- When I see someone post as a letter avatar, I sometimes direct message them with a link to that topic.
I held off on doing anything like #2 for a long time, but it’s proven to be far more effective than #1 alone.