It shouldn't come as a surprise to anyone: if it has hardware and an interface, a hacker can hack it. That shouldn't scare you. If you're reading this, then you're on a digital device that could undergo the same fate. It's the nature of the beast.
The truth is that most hacking is done due to lapses in security, way-too-simple passwords and logins, or through a weakness found and exploited in outdated software that is still being used.
The first step is to make sure usernames and passwords are not easy to guess, and are not left out and about. If you have a Post-It note on your computer with the username and password of digital signage software, there's a fair chance that it is more susceptible to being hacked. Also, if it's any of the most frequently hacked passwords or the combination of your luggage, those could also lead to easy hacking.
The second step is to make sure the software being used is kept up to date. This includes the signage software on the computer, for the signage itself, as well as the network in between. If the hacker can get into the network, he/she might not be able to change the signage messages, but he/she could prevent you from doing the same.
The final step is to make sure your processes are up to date. For example, make sure there is a procedure in place for the computer that has the digital signage software. Let's make sure it's not the same one the intern uses to sort data, just in case the intern spills coffee on it. Also, make sure their are procedures for locking screens, locking rooms, and that only trusted employees are given access to the machine.
"Life moves pretty fast. If you don't stop and look around once in a while, you could miss it."
And he hacked his school's computer with his IBM PC XT, an infinitely less powerful machine than even the basic cell phones today. Imagine the trouble he would be getting into today's tech world.
The point is, keeping up with the speed of today's tech world can feel daunting but don't fear, the good guys are working on today's security as much as the bad guys.
In the meantime, some bonus reading on digital signs being hacked: