I was happily oblivious for a good long time, although I thought he was generally pretty clever. Cute too.

But early signs were on the very-subtle side. He was more often late on the really obvious stuff...
So - he walked late (17mos), talked late (22-23mos), was generally late on all the gross motor stuff that dominates early development charts... but on the other hand he was really "engaged" with people really early and was always ALWAYS involved with what was going on around him, his fine motor skills were way ahead from very early on (although it doesn't seem to have translated into nice handwriting...), and he was obsessed with books from infancy. I didn't realize at the time that having to prop up your not-yet-sitting-independently 6 month old so he can look at his very favorite book AGAIN for half an hour at a time, carefully turning the pages and studying them... isn't really that common. It was a DK cat book, about 150 pages, hardcover, with pictures of all the various breeds. I still have it in the baby box.

But I think my first smacked-in-the-face-with-it moment was when he was two and we were visiting my sister and waiting for her to have her first baby (two weeks late!) We were in Colorado for the first time, and we had just decided to homeschool him, so I took advantage of the location to pick up some books we couldn't get at home in NC -- the Singapore Earlybird (K4/K5) math workbooks. I figured they were for later. I was mistaken. LOL It didn't really seem weird to me that he could do them, since it was pretty straightforward stuff, but there was one exercise about conservation of volume... which is a classic Piaget thing that isn't supposed to be "there" until something like 7 or 8 years old and I thought, "oh this should be good..." but not only did he get it, he got it without any kind of explanation, and explained it back to me! eeeek! I had never been a fan of Piaget, but that was the first time I thought, "uh oh..."
By the time he was six I was pretty sure -- he flew through curricula at top speed, he had been reading well forever (words at 2 or 3 and books by 4), and he was finally letting on bits and pieces of what he could do to others, so I didn't feel like Jimmy Stewart in
Harvey anymore

We were concerned that he had some verbal quirks though, which is what led us to test... and I wouldn't have guessed more than "MG" myself before then. Not that I knew there were sub-levels, but I never really thought he was "that high", and I fully expected him to completely take a dive on one section or another.
Even now I think, "Well he could take an AP test... but it's only Stats.. that's not really that hard... not like Calculus..." and I'll probably continue to do that forever! LOL I could probably pop along perfectly happily without considering IQ at all (I mean other than a fascinating statistical problem... lol) but that we have to deal with other people sometimes. At home on our own we just do what we do, but try to participate in anything else anywhere else and I'm glad I have a test report to remind me that I'm not making this up!