Fresh ham vs. Pork shoulder

Earlier in the spring, a friend who raises hogs gave me a "butt" when she had one of her pigs slaughtered for her family. When she gave it to me, it was huge, but I didn't think much of it and threw it in my freezer. Now that I thawed it (and I have 25+ people come for pulled pork in two days), it looks more like a fresh ham. It has bone end on each end and one on the side and weighs about 25 lbs.
I guess my question is how do you identify the front shoulder (butt) from the back leg (ham)? I like to know in advance if I should expect pulled pork or sliced pork. I guess that would be the main difference in the end.

looks like a ham ..

A ham will have the round rear leg bone running through it. A butt will have a flat blade bone. A whole shoulder will have athe round leg bone that runs through the front leg (aka 'arm' or 'picnic') attached to a joint plus the blade bone.