My take is that although apps are a reality and can come pre-installed on a phone, they may not fit into the end game the larger market of superstores. I agree with 10bagger with repect to having an app for convenience stores...people will simply not take the time to app it up to save on a chocolate bar.
The huge chains of box stores on the other hand are already linked to a centralized system that transmits information from the central office to each individual store and back again to HQ. From the music they play, to the daily deals, to inventory tracking, the individual businesses have their own unique and separate systems. If the iSign antennae are installed through the individual stores and plugged into the existing backoffice tracking that is already occurring, HQ will have another useful and UNSHARED marketing resource at their disposal without having to rely on the likes of Apple/FB/Google to transmit results to them for what could be an outrageous premium (I am speculating here). Knowing a few people who work in the central office of a few big box stores, they rely heavily on their own systems to transmit valuable data back to HQ.
I am not saying that the big boxes will bite on this technology as they may already be satisfied with their tracking that is occuring at the register with their existing systems, but I am saying that iSign does not have as much of an uphill battle regarding proximity as the other GPS proximity solutions may have.
This is of course my opinion. I remain long and iBelieve.