There are a couple of science and science fiction authors that started posting hashes or signatures for their predictions for the future, and then post it after events played out.

I think the idea is that unlike pundits predicting the future, you don't want your particularly clever friend speculating out loud ten minutes into the suspense movie what they think is going on because they either guess the ending, or their guess makes you figure out the ending, and then it's 70 minutes of sitting there reading all of the other foreshadowing and not getting to enjoy any of it.