I could tell immediately that he was special when I put on his youtube compilations in late 2011. The only question was his height, but as I researched the actual reasons why short QBs fail, I kept discovering that Wilson had the tools and skills to beat those obstacles. Then I learned that his line at Wisconsin was taller than any line in the NFL that year. That was my moment when I knew he was an extremely exciting prospect.
As far as a Seahawks performance, I think Atlanta impressed me the most with Chicago and New England being close runner-ups. In terms of the "you knew" moments during the season though, I'd name two: Kansas City in the preseason and Dallas in the regular season.
Prior to the Kansas City game, the Flynn backing crowd had one good argument in their arsenal, that Wilson hadn't yet faced starting defenses. Not only did he face KC's starters that week, but he played them in the week 3 "dress rehearsal" game where both teams tend to be pretty serious and use more than just vanilla schemes. In what I would argue was the biggest game of his life (knowing that his entire career path was hanging in the balance), Wilson didn't just impress, didn't just dominate, he flat out embarrassed the Chiefs. He throttled them. It was as much a "no doubter" moment like any I have seen in Seattle sports history. That game not only made Wilson the starter, but it made him the story of the preseason.
The reason I also mention Dallas is because Wilson badly struggled in week 1 against Arizona and yes, height WAS a factor in those struggles. Dallas was coming off a huge win at the Giants and at the time looked like they'd end up a 10 win team. Wilson bounced back that week, basically proving that the preseason was not a fluke. That was the moment my final doubts left me.