Anyone can recognize a crow when they see one, right? Maybe, maybe not.
Common Ravens, while larger than crows, can appear awfully crow-like to the untrained eye. I've also heard of people mistaking the smaller Common Grackles for crows. But even if you don't make those mistakes, it can be very difficult to tell an American Crow from the similar Fish Crow (pictured above), at least by appearance alone. This is a case where a bird's voice can help to eliminate confusion.
Common Ravens Croak.
Common Grackles Squeak.
American Crows Caw.
And Fish Crows make a short, nasal Uh or Uh-uh which can sound like this:
While the above is a gross generalization (crows, ravens, and grackles are all well-known for their complex and diverse vocalizations), these brief descriptions provide a handle for their commonly heard calls. I should also mention that the begging calls of young American Crows can sound similar to Fish Crows, but this is only an issue in the summer.