WWI German Maltese Crosses - officially the WWI cross insignia was meant to be a plain black, but most German squadrons preferred to paint the insignia with a white border, presumably to aid visibility. This sheet provides markings in that style.
These decals are scaled to represent 30", 36" and 48" sizes in 1/300 scale. (They're also ideal for large aircraft in 1/600; equivalent to 60", 72" and 96" across.) The actual sizes are 2.5mm, 3mm and 4mm.