Informational signs that make money let people know enough stuff about what they would like to purchase, to make them want to buy it. This type of sign would also entice people to come in for a special that you might have.  It could even get people to make purchases that they didn't even have in mind until they saw it.   Sign types typically used for this type of display are:

Backlit Displays, Banners, A-Frame Signs, POP Displays, and Laminated Foamcore Signs