The game board reserves a space for Event cards, but how they come into the game is a secret, thus spoiler protection below.
The "sign the board twice" envelope introduces the Event cards, with rules concerning them to be pasted into the rulebook. I know this from an earlier group. My current group has not yet opened that envelope, but we did just open the "all nine minor cities" envelope, which contains a few event cards like Resistance and Riots. Are we supposed to play with those few event cards now, or set them aside until the rules take effect?