Social proof is public social engagement that other users can see. This includes likes, comments, and shares of an ad. It can also include award wins, reviews, and other forms of press engagement. These interactions can matter just as much as the ad copy when it comes to building trust and credibility.
Who's done it well
See who’s doing this well in travel.
Some form of social proof should be applied to all ads, whether it’s a number of how many have bought your product, a review rating, reference to an award win, or a press snippet. For best results, social proof signals should be overlaid on top of your image for maximum visibility.