I noticed an answer referring to a diamond moderator by username, and the ♦ was included as if it were part of the username rather than a separate symbol. I was going to edit the post to remove it, but I wasn't sure: maybe that is part of the username, just like the "Dr." honorific is a real part of a doctor's name. Should I regard the symbol as part of the username when quoting someone myself?
It's not part of the username.
You can tell this by going to any moderators' user profile.
When you're on the profile page of a moderator, you'll notice it says their name : ex: Shog9 (then moderator ♦)
When you go to the moderators user page, which lists all the mods for a site, https://stackoverflow.com/users?tab=moderators, you'll see that the diamond is not underlined when you hover, only the name.
So it's not part of the name, but you're free to include it when referencing a moderator in a post or comment, just out of respect or whatever.
No, the diamond is a decoration, not part of the name. Somebody was probably just being cute -- either that or cut/pasted and picked up more than just the strict name.
You can confirm this by starting to ping a moderator in a comment or in chat -- the name completion after the
@ does not include the diamond. (You'd also be able to see it in the "edit profile" interface, except you'd have to be a mod to do that so that doesn't help many people.)
The diamond is attached to the end of the username when displayed by the system. This includes the top navigation bar, user pages, and the user card below each post. The diamond in the post was added by the poster.
However, I'm not sure why you'd remove it. The diamond easily communicates that the user is a site moderator, and removing it would not only eliminate that communicative element but would also be a minor edit, bumping a post to the top needlessly.
It's common for users to do this in meta discussions, and I've never seen it be a problem.