[worewood]

Should have done a clear banner, with maybe a red or yellow border, and an icon. Preferably inside the content area, just like Wikipedia does on disputed articles or current events.

His banner has stylized fonts, a photo as a background, and as such looks like an ad or something decorative.

[vermilingua]

Exactly this, the infobox is common to effectively every wiki for purposes exactly like this one. They’re using mediawiki as their engine so they already have the support baked in.

[Blackthorn]

They used to have one on every page, but the creator of the website (for some reason I was never able to figure out) hated how it contained authorship information so he removed it from every page.

My own wiki puts the "this is homebrew" information in said infobox, and has never received a single complaint about people mixing up homebrew and official content.