Some of the ways to tell the maples apart without cutting into them are:
By the seeds. Sugar maples seed (we called them helicopters) in the late summer or early fall. Red and silver maple seed in the spring.
By the leaves. Red and silver maple leaves are much more deeply cut than red or sugar maple. Sugar and red maple leaves are much more similar to each other, however the cut between the lobes on a red maple tends to be sharp, while the sugar tends to be more rounded. This is a little hard to see at first unless you know that you have one leaf from each to begin with.