You have a time machine but you can only use it to send one post back in time to /a/.
What picture/text would you post and how far would you travel back in time?
What else would you use a time machine for?
I would send a list of all the places where major tragedies happen, such as 911, and then the dates they happened.
Then I'd say something like "your true love will be here" and send it to everyone i could