Restaurant Testimonial Drawings

I ate lunch in this restaurant today and their "drawing testimonials" hit me with a marketing insight. How can you make it FUN for clients to give you testimonials? This restaurant had decent food, but there's no way they would've gotten all these testimonials if they didn't make the process fun. New customers see the colorful drawings of hundreds of other travelers on the wall, and it makes them want to create one of their own. I bet many people make drawing testimonials while they're waiting for their food (before they even taste it!). Clever!