“What are some of the most effective ways to utilize smaller surfaces for signage or projection?”
I think form factor has as much to do with effective utilization of small surfaces as anything else. Projection typically requires finding a space to mount the equipment, and if you have a small surface, the odds are that you probably have a small space to work with. In my humble opinion, I think small form factor screens like tablets or iPads are the most effective way to utilize small surfaces for digital signage. In addition to their size, the CPU power, potential for connectivity and interactivity provide flexibility in deployment for a variety of use cases across different verticals.