Zane,
The first cannon is an M1857 12-pounder (weight of projectile) bronze Napoleon, and the markings that can be seen on the muzzle face represent information about this individual gun. The number 330 is the U.S. Army Ordnance Registry number given to the piece when it was accepted, the initials T.J.R. are for the man that inspected the gun (in this case Thomas Jackson Rodman), 1,230 lbs. is the weight of the barrel, and the year it was manufactured is 1863.
The second gun is a cast iron 4.2'' (diameter of bore) Parrott rifle, and R.M.H. are the initials of the person that inspected the barrel, 4,260 pounds is the weight of the tube, No. 392 is the Registry number, 1865 is the year of manufacture, and W.P.F. denotes that this barel was made at West Point Foundry.