I had to work out how to deal with other parents' comments, too, especially when he was about six months older than your little one and signing up a storm. I think I actually got some good tips out of a post in this forum back then. My general tactic is not to go out of my way to bring up things that my kid does that are advanced, but not to downplay them, either.
As for my son at that age, he was extremely alert as a baby. He has always had a long attention span, and loved having multiple books read to him at a very young age. He was early on a lot of his really early physical milestones, then late on some of the middle ones for the first year (rolling over, sitting up unassisted...I think I may have held him back on these a bit, at least the sitting, out of my first time mom paranoia), but then as soon as he sat up he was the first baby in our moms' group to crawl and then walk, and he's been early or on track with everything since, as far as I know. To be honest, he almost immediately figured out how to run, and I haven't had as much time to study early childhood development as I once did. :) He started life being able to make a number of sounds he wasn't supposed to for months, and he's turned out to be very communication-oriented.
The signing is awesome! I find it really sad that everything with kids gets turned into a competition - like, if your kid is advanced, then their kid is automatically behind - can't we just respect that kids are kids, that they have different talents, etc. and celebrate them all???
Anyway, cloudbutterfly, your son sounds like mine! He was the most alert baby, making perfect eye contact and smiling at everyone in the delivery room moments after birth. He rolled over at his 2 week check-up and scared the crap out of the doctor! He, too, loves books, and has had a voracious appetite for them since he was just a couple months old - multiple books in a sitting, started "reading along" by 4 months, and he mastered the lift-the-flap kind by 6 months. He could turn on our cell phones by 4 months, started saying, "Mama!" and standing/walking with support at 3 months, etc. Naturally, I think he is gifted (haha!) but time will tell - in any case, he is the most awesome, energetic, intense child! He is just STRONG - personality and physicality! Everyone is always commenting on how intelligent and different he is (unfortunately, sometimes with a less than totally positive connotation...a lil bewildered, at least!).
OP, I think it is awesome that you are vowing not to apologize for your child's accomplishments! I agree with you and cloudbutterfly - no need to rub it in, but no need to be afraid of it! The fact that mentioning our children's accomplishments is seen as patently insensitive is a sad thing - and it harms the kid. I was always ashamed - I hid my report cards when my grades were too high, and I failed every spelling bee on purpose at the crucial moment to avoid the (negative) attention - it was really sad and burdensome.
On last thing - as a kid with an eidetic memory, it can come in handy! I was always in demand to settle toy disputes as a kid, because I was the only one who knew that so and so's Barbie's eyes were a little closer together than the other one, and could always sort out identical toys when they were mixed up and get them back to their owners (based on a tiny scratch, etc.). I was also able to help my sister with her homework (she is 2 years younger) because I could say, "Ok, turn to this page, third paragraph down, under this heading - re-read that and that's where the answer is" - without ever looking at the book, because I had used it two years prior. It also REALLY helps with those last minute college cram sessions - being able to stare at the book and then "read" it later in my head when writing essay answers was essential!