BrightSign players go through a number of revisions ("revs") during the hardware production lifecycle. Revs are lettered starting with A (e.g. "rev B", "rev C", "rev D").
If you want to know the hardware rev of your BrightSign player, locate the device serial number (the easiest place to find the serial number is on the label located on the bottom of the player). The third character in the serial number is the hardware rev: For example, the serial number "33H769000122" is a rev H of the player model.