Is there a way to prevent users from signing up with certain words in their usernames so they can’t imitate our moderators or fake an official account?
Hello, welcome to Meta! 
I believe, the reserved usernames setting is what you’re looking for:
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where can I find this setting?
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That looks like the mod view, are you sure you’re admin?
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You need to be an administrator to change the site settings.
This is the moderator’s view you’re looking at.
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