Anyone interested in customisation, whether of minifigures, tiles, bricks or anything else, may be interested in this clever use of LEGO parts, if they don’t know about it already. This is a decal application tool, created by The Cooper Works, for applying decal stickers to elements.
The main aim of using this is to be able to apply decals without having to worry about air bubbles or smudges, which can completely kill your work. It looks like it’s mainly for applying decals to tiles, but can probably be adapted for use with bricks and minifigures.
As well as being able to download instructions for the decal tool, The Cooper Works also sells a couple of military-themed decal sheets in their shop. Go check it out!