What is the most representative way to measure the impact of a digital signage deployment?”
I believe that the metrics will vary depending on the objectives of the group, but the methodology to get there may be very similar. Knowing the goal of the implementation is key as is identifying the metrics that need to be measured. Having established both, create a baseline and measure impact of the digital signage versus traditional advertising methods. The results should provide data that represent the change between your digital signage messaging and other traditional communications channels.