The yellow bracket is intended to prevent the installation of skimmers. Unfortunately, the design isn't compatible with all of the fixtures they're applied to, and are often enough just not installed correctly... but that's what that part is sold as.
Such a little thing, but: the Rules Reference card in introductory-level Magic: The Gathering products. Magic's full rules are 250 pages of legal-lite text, and yet, this little folded insert, with just five cardface's worth of text, amply covers everything a complete beginner needs to play. It's a brilliant example of cutting an explanation to the bare minimum and piggybacking on background knowledge.