The letter on it's own was used very early on to represent the (P)riest class, which actually appears to be functionally identical to the (P)rofesional class of the modern world, used as a source of expert authority for interpreting everything from natural phenomena to law.

Q mentioned it I believe. From my own research I've learned that the letter alone was used very early on to represent the (P)riest class, which actually appears to be functionally identical to the (P)rofesional class of the modern world, used as a source of expert authority for interpreting everything from natural phenomena to law.