There is a common myth that exists that making your images for digital signage at a higher DPI will increase the quality of the image.
This is in fact just that, a myth.
The only factor that matters when creating an image for digital signage is it's resolution in pixels.
An image at 1920x1080 at 72dpi will look exactly the same as an image 1920x1080 at 300dpi or 3000dpi for that matter.
DPI is a measurement for print, and is irrelevant in a digital environment.
There is however one thing to be mindful of, when creating an image in certain graphics applications if you create an image and specify 1920x1080 as the pixel dimensions then change the dpi to 300dpi some graphics applications will actually produce an image far larger than 1920x1080.
Because of this we recommend simply specifying 72dpi - this is the safest way to make sure the file is going to be the correct resolution.
You should also check the resolution of the resulting file (right click and select properties on windows or get info on a mac).