Not sure what you mean by motifs in the context of folk art. There are recurring symbols each with their own heritage. I'm not trying to be obtuse but it's not simply a case of saying people in Sussex liked painting egg and dart patterns or fleurs de lys and those in Durham painted trefoils and ducks. There will be a historical reasons and probably a technical one too depending on the medium.

You could look through some old folk rock covers from the 1970s but they'll tell you about 70s culture, not ideograms and cyphers of the native culture.