Section 2 sets the outer boundary of the whole zero rate: the words in Group 3 are used in their ordinary everyday sense, which means they are restricted to goods produced on paper and similar materials such as card. Vinyl, PVC, mesh, fabric, foamboard, aluminium composite and correx are not paper or card, so nothing printed on them can be a book, a leaflet or a brochure however much text is on it. There are two exceptions in the notice and neither helps a sign: children's picture books may be printed on plastic or textiles under 3.7, and maps may be printed on other material such as cloth under 3.10. Display makes it standard-rated twice over, since 4.1 standard-rates sheets intended for public display.
What decides it?
The substrate. Paper and card only, apart from children's picture books and maps.
Where does this come from?
HMRC VAT Notice 701/10, section 2, HMRC's guidance on zero rating books and printed matter. See the notices we work from.