Hiding usernames from users not logged in?

[XFFA.IR Bot]

In the forum I moderate, use of real names as usernames is mandatory for everyone who actually posts. Recently, though there has been some discussion about the privacy aspects when one member who feels strongly about this, discovered that his name was also visible to visitors who are not logged into the forum. (Quite why he had assumed otherwise is beyond me, but that’s not really relevant, I think.)

So, my question is: Is there a way to hide or abbreviate usernames, except to users who...

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