What is the most representative way to measure the impact of a digital signage deployment?”
Impact depends on the objective of the signage deployment! If you didn’t have a documented and measurable objective, then you have no concrete evidence of impact. Brawn Consulting offers a great class on signage project management, by the way, and the class dives into the nuances of return on investment v. return on objectives for the digital signage world. For power users like myself, measurement and impact for signage deployments are based on onsite client satisfaction (employees), savings on resources (reduction of parallel efforts and support costs) and content campaign successes (how many eyeballs, when and where). In the end, if the deployment doesn’t have hardware issues (support calls) and displays the right content to the right location at the right time, then it’s a success!