Carrie, you’ve got what I call a “good” problem. You must know, from your own observations and comments from others, that his behavior is very rare. Judging from the evidence you offer (his ability to find the letters in print matter he hasn’t seen before), I am willing to conclude that this is true knowledge and not just chance.
Want to hear a wild story? Around 400 B.C. the great Greek philosopher Socrates proposed the theory that all knowledge is recollection of things learned in previous existence. He “proved” his theory by leading a totally uneducated slave boy through logic steps that enabled him to verbalize the Pythagorean theorem (a squared + b squared = c squared). The boy “had to have known” it before and was now only recollecting the previous learning. Socrates would have loved to hear about your son!
But, out of the hypothetical into the real, you will have a continuing challenge throughout your son’s life to strike a balance between providing enough enrichment and avoiding pushing. For now, talk and exposure to new objects and experiences—and giving him plenty of love and security—are your main tools. Converse with him about routine activities (“Mommy’s going out to the garage to get some paper towels, and then I’ll fix your lunch”), emphasizing what might be new words as you say them. Don’t forget the verbs; they are just as important as the nouns.
Certainly you will want to read to him every day, probably several times. There are now many wonderful books available for infants and toddlers. Take him to the library regularly, point glowingly to all the books and choose three or four of them for him. I would also encourage your son to learn to strike the keys of a computer. The keys are identified by uppercase letters, which are the ones he recognizes. I predict that he will delight in having the letters appear on the screen after he hits the keys. And don’t allow his enrichment to be only verbal and literary. Make sure he has toys that will improve eye-hand coordination and problem-solving (blocks, beads, puzzles). You didn’t mention whether he walks yet, but regardless of whether he does, get him toys that make walking and other large muscle activities more exciting. The Corn Popper™ is my favorite.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.