In digital signage, in most cases, 24/7 is a must. Power failures may happen and in some place they just plug off the power when they close the place in the evening. This means you need your digital signage player be able to wake itself up, or “auto start” itself.
Some Android players (especially dongles) do not have a power on/off button, so once you connect them to the power or when the electricity is back – they are turned on.
The problem is with devices which do have an on/off button: many of the TV boxes, such as the TV boxes of Minix Neo series, do have that button. So, how do they get the auto-start ability? In case of Minix, you can, physically, open the the box, remove the board and change a jumper there to the auto-start mode (as can be done in Minix Neo X7, using this procedure). Some of the Minix TV boxes, such as the Minix Neo X6 do not have the ability to be jumpered to auto-start, that is we find them not so good for digital signage. Some devices may be ordered from the manufacturer when they are already set to auto-start, as the Minix Neo X7i (make sure of that, when you place your order).
In some other devices, one can set the auto-power by software, that means in the Android settings.
All in all, no matter which signage player will you use, before you go to pick one, better check if it has the auto-start ability.