“What are the keys to integrating digital signage with mobile devices?”
I think you have to be careful what content you intend to use in both digital signage and mobile. Some things that may work great on mobile do not translate that well between mobile devices and digital signage. I think one of the keys is to have ideas that actually work in both mediums. This sounds so basic, but it’s true, and integration between the two mediums is easier said than done.
Also, I would recommend testing your content to make sure it works in both places. The worst thing is to have something that works great in mobile, but looks like crap in a much larger format.