First:
In all of Artillery history, there is no historical document record of any cannonballs being marked with raised numbers or letters.
Second:
The brass screw-in plug in the side of the ball means it was manufactured to be a Counterweight. The plug lets to add the precise amount of weight (sometimes sand-grains, sometimes lead pellets) to make the counterweight-ball weight exactly what you need it to weigh.
If you care to learn any more info about how to distinguish an actual cannonball from the many versions of Civilian-usage lookalikes (Sports Shot-Put balls, gatepost-top balls, rock/ore-crusher balls, large ball-bearings, etc,), read the educational article (with helpful photos and diagrams) here: SolidShotEssentialsMod
Georgivs, your vote that the ball is a Shot-Put ball indicates you looked at the ball photos but did not read the text Kertj1 wrote, which says the ball weighs 20.54 ounces. There's no such thing as a 1-&-1/4-pound Shot Put -- nor anywhere close to that lightweight.