Junk is right about the Red Ear Slider. They have a distinguishing red mark where their ears would be. A female RES will generally grow to around 10 to 15" in length. The males are smaller. A RES will bite at times, so don't just assume that they will not. It is rare to get a box turtle to bite you without considerable provacation, but the RES will give you a nibble without much warning. However, just like the snapping turtles generally found in most ponds, they are not likely to be able to do much to grown man with relatively tough skin. Contrary to popular belief, even a snapping turtle that is a foot across will not take off your finger.
Have you ever seen anyone "noodling"? That is where guys walk around in water and try to get large catfish to bite onto their arm as a way to catch them. I've done that with snapping turtles many many times. Sometimes they are a bit contrary about letting go. A match or lighter to the tail almost always gets them to turn loose though. /forums/images/graemlins/grin.gif
One of the most distinguishing features of most every known snapping turtle in north America is the jagged rear of their shell. If the rear of the shell is serrated looking, the turtle will make it a point to bite you if disturbed. If your hands are not fairly tough, just wear a pair of gloves and get the turtle to bite your hand. It will hang on long enough for you to pull him out of the water. Also, unless you are holding a snapper by it's tail, it can bite you. As I said, the bite is not as bad as legend has it, but I wouldn't try to kiss one. A friend did with a decent sized snapper and he basically became a hare lip. Even though even a fairly large snapper cannot bite hard enough to really hurt my hands, I wouldn't want to offer up any soft tissue to be bitten. /forums/images/graemlins/blush.gif
If they are an issue, yes, you can blast them off of logs while they are sunning. But, unless they are making a noticable impact on your pond, I would generally let them be, or relocate them. Unless you literally blow their head off, they will live, and suffer, for several hours if not for several days. They are a hardy lot, and have not changed much at all from the days when dinosaurs ruled the earth. If reasonably possible, I let them live.
If you don't believe me about their bite, try to get them to bite you on the hand when you have a pair of leather welding gloves (or something similar) on first. After a while, you will realize that they are not like sharks with a shell.