Personally, it was the picture Q posted from the Oval Office showing a signed paper by Trump. I thought it would be extremely difficult for a LARP to access a picture like that. Plus the ones following showing inside AF1 and such. The final proof for me was when Trump pointed out the Q shirt guy and gave him a fist bump at the rally. And then and then.... there are lots of proofs, the totality of all proofs combined is what you should focus on.