He couldn't tell the diff between M and N, and S and T, and G and H, but heck, I'm not sure I would get those right either since those sets look very much alike! Other than those pairs, he was remarkably good at telling me what letter I was signing, which amazed me. I call him baby-ham-hands in my head sometimes (because he's still adorably clumsy in that early toddler way, and his fine motor is pretty slow in developing), so I've never even thought to work with him on signing the alphabet, but we have watched Signing Time, Volume 5: ABC Signs hundreds of times (that and Curious George Learns the Alphabet are how he learned to identify letters) and by golly, he learned to read the signs as well as the written letters!
Go baby Jackson!