Whats with the '9' on the grips on some artillerys?

[Lugerdoc]

The first 60K 9mm brooms were made at the Mauser factory WITHOUT the "Red Nine" marked grips. As stated above, due to the confusion with the 1915 military 7.63mm order, Mauser did make them later on with the large branded Red Nine. Many of the early ones were then marked by field armours with various size Red 9 markings, but be careful of fakes, particularly if both sides are not serialized inside to the pistol. Tom