From the Guardian:
In a move designed to coincide with the pope's visit to Britain in September, London buses are to carry posters calling for the ordination of women.
The initiative, from the UK group Catholic Women's Ordination (CWO), will see buses carrying the slogan "Pope Benedict Ordain Women Now".
According to the weekly Catholic magazine the Tablet, CWO has paid about £10,000 for the posters to appear on 10 buses for a month from August 30.
The pope will be in the UK from September 16, spending two days in the capital, and the posters will appear on routes that go past Westminster Cathedral and Westminster Hall. Both venues feature on the papal itinerary.
....
Buses have become the preferred vehicle for believers and nonbelievers to promote their cause to the wider public. The trend started in January 2009, when a group of atheists arranged for an "upbeat and positive" message to counter slogans of hellfire and damnation from some churches.
The ad campaign by the Catholic Women's Ordination group will counter the Vatican's recent classification of women's ordination as a delicta graviora (more grave crime) against church law.
As expected, the Vatican also updated its list of the "more grave crimes" against church law, called "delicta graviora," including for the first time the "attempted sacred ordination of a woman." In such an act, it said, the cleric and the woman involved are automatically excommunicated, and the cleric can also be dismissed from the priesthood.
I predict that delicta graviora will soon become household words. "Stop tracking mud into the house! That's a delicta graviora!"
Thanks to Ann v. for the link.
UPDATE: Erp in the comments points out that ads appeared in buses as early as 2007 for the Christian Alpha Course.
The commercial will appear on screens in hundreds of bars nationwide and hundreds of buses in London and Birmingham.