Data security is protecting the information a platform holds and the systems that hold it. For a screen network the risk sits somewhere people rarely look: the players.
A signage device is a networked computer in a public place, often physically reachable, frequently forgotten in patch cycles because it is not on anyone's laptop inventory. It holds credentials for the management platform, sits on the corporate network in many deployments, and is the least-monitored thing in the building.
The caveat is that the headline risk is not the data on the screen; it is the screen as a route into everything else. Put players on a segregated VLAN with no path to internal systems, treat their credentials as compromised by default, and include them in the patching schedule. A display showing public content is not a public-risk device.
The blog covers the platform side of this in more depth for video: data security and privacy in automated video.