It could mean a number of things. There's no real way of telling without knowing all of the markings on the rifle, and where this marking is placed.
It means the action of the rifle was made by Mauser or copied by someone.
It means the action of the rifle was made by Mauser or copied by someone.
There are various numbers, including the serial number, proofing marks, and caliber. Most Spanish Mausers were chambered in 7X57.
Square top vs round
Depends on the country of origin.
Maker's code, indicating that the pistol was made by Mauser.
It means your rifle was made in 1938 at the Mauser AG plant in Obendorf. 42 was the code for Mauser- many different firms built the K98.
Do you mean 7.63mm Mauser, or perhaps 7.65mm parabellum? There is no 7.65mm Mauser, but the 7.63 was based on the 7.65mm Borchardt. Either way, it is a bottleneck cartridge, while .32 ACP, also know as 7.65mm Browning, is straight-walled. The two cartridges are in no way interchangeable.
Let's use the correct term. The 7mm Mauser fires a 7x57 CARTRIDGE. The bullet is just the part that comes out of the barrel at high speed. The 7x57 name means that it fires a bullet that is 7mm in diameter from a cartridge case that is 57mm long.
The most likely answer is that "US 1906" is what it is chambered in, meaning the US .30 of 1906, also known as the .30-06 Springfield.
whats a mean number
Define 7mm. Do you mean 7mm Mauser ( a little less than 30-06), or 7mm Magnum, (a bit more than 30-06)