1/144 decals for WWI aircraft.  The squadron sheets were designed originally for repainting various now-OOP models from the excellent Wings Of Glory line, but can of course be used with metal kits or the increasingly popular 3D-printed aircraft from various designers on Shapeways.  The generic national markings sheets are simply roundels or crosses in a variety of sizes - 8 each of 4mm, 5mm, 6mm, 7mm, 8mm, 9mm and 10mm across.  These are suitable for the vast majority of single-seat aircraft in 1/144 scale - I hope to add some larger sizes at some point for bombers and observation aircraft.