I've also done this 'reply to someone else's hashed prediction so they can't edit it' thing before. There were some other suggestions of how to verify hashed predictions in that discussion, if our asterisk-free comments seem insufficiently secure for dealing with User!Quirinus_Quirrell.
I would like to make a prediction, but I'm not ready to raise the subject of the prediction just yet. So to show that it was not just obvious in hindsight, and to strengthen my precommitment to write an article about it later, here is the sha1sum of my prediction: 9805a0c7bf3690db25e5753e128085c4191f0114.