Rumors are created by the DM, sometimes as the result of player action.
I never really doubted that rumours were of two different calibres. The true rumours, created by the DM's and the political jibberish of the players.
However, since Bjørn clearly states that you can only create rumours via the DM, then any other IC information you wish to spread, should be in the form of either dispatch, decree or posted in the Bard.
The Bard isn't exactly the best place for these things however... Only if you actually make it into a riveting tale of some sort, not just political statements, will they be welcome.