Could be a Mzee Pakistan made saddle.
I used to have a guide that told a person what the numbers mean on a saddle (western and english) but I have lost it.
Usualy the 402 is serial number and the :19 indicates seat size. But with some of the imported stuff from the middle east these numbers may not be exclusive to anything but the manufactuers no. Ie: # 19 out of 402 made.
If you want to know seat size take a measuring tape and measure from the pommel button back to the center of the cantle and this will give you seat size. If it measures 19 then the :19 is the seat size (pretty big and not a common seat size in English saddles.
I am pretty darn sure that this is either made in Pakistan or possibly India but my first guess is Pakistan due to style features, type of leather used for the billets, leather quality and Pommel shape, stitching etc.
The seat looks rather flat in the middle are you sure the tree is solid.? To check if the tree is solid rest the saddle pommel on your hip and pull the cantle towards your body. If it gives (the seat forms a crease in it) or moves then the tree is either fractured or broken. Pakistani or India made saddles are built on solid wooden trees and not on spring trees. (Spring trees will give some)
It is an AP (All Purpose design) A common design with Middle East saddles.
What did you pay for it if you don't mind me asking?
Did you look under the skirts (The flaps that cover the stirrup bars) up by the pommel for a makers mark/plate??
I will research this more indepth when I have more time. That M is not familiar with me but Pakistan and India are known for thier knockoffs. India used to have a knockoff Mark series a long time ago but I don't think it was associated with the letter M as etched on this saddle.
"The question is not, can they reason? nor, can they talk? but, can they suffer?" Jeremy Bentham