RAF WWII. Sky code Numbers 18′ , 24′ , 30′, to go with Sky code letters on X72189.RAF Yellow Prototype P. 4 sizes of the letter P in a Yellow Ring, 26′ and 30′ in four styles, 36′ in three styles and 54′ in two styles. There was no official font used so they could vary between manufacturers.(RAF codes/RAF code letters/RAF serial numbers) [Prototype ‘P’]