The majority of existing digital signage systems are expensive and also require power and data installing which can add to the cost.
The low power sleep modes of Atmel processors along with the likes of low power e-Paper display technology however could make a battery-based solution feasible. Low power wireless could potentially avoid the need for physical data wiring to the display.
Smart energy gas meters use Lithium thionyl Chloride cells which can power a ZigBee transmitter at 30minute intervals for around 12+ years which means that it should be possible to power a e-Paper display for at least couple of years before needing to replace the batteries.
Uses for this could include room booking information on meeting room doors, timetables for transport, wayfinding, etc. where the information may only be updating infrequently.