It widely depends on what you want to show on your signage.
Is PowerBI the only service you want to show on your display?
We have multiple screens setup in our office and they are all connected up to one PC (Windows 10) via a splitter. You can have PowerBI open up on Google Chrome with an automatic refresh on a timer (Chrome Plugin: Auto Refresh) with a program called "AutoIT AutoTab" that switches windows open on your desktop on a timer.
You can also make PowerBI open reports in a "Windowless scheme" by adding ?Chromeless=1 at the end of your URL.
In my experiance, I've never found decent Digital Signage software that does what we want it to. We have always used a "Windows" solution.