These days, you can spend a lot of money buying really nice digital signage tools. And if you’re doing so, then you likely have some pretty dynamic content you’d like to load. Something that doesn’t necessarily lend itself to a dynamic content platform, but which is nice for the quick presentation that you whip up and want to use for a form of digital signage is Keynote presentations. These are inexpensive and can be played on monitors through AirPlay or directly through a Mac Mini connected to a television or big monitor. Great for a monitor in the company lobby, the hallway in the school or for subliminal messaging at…