This might have the potential for an interesting ad campaign but you would have to find a way around the bureaucracy to do it:

That 50-foot message, visible to thousands of commuters on a nearby freeway, was projected Wednesday evening on a dark portion of the bell tower of the Cathedral of Our Lady of the Angels.
The sign was gone within hours, but the Los Angeles Roman Catholic Archdiocese was not amused.
“A church tower is different from a billboard. If it wasn’t, we would have been selling ad space 2,000 years ago,” spokesman Tod Tamberg said.
However, the sign wasn’t really trolling for advertisers. It was a guerrilla art piece by James Cui, who included a telephone in the projected image.
“I’m flattered you noticed,” the 28-year-old Highland Park graphic artist told the Los Angeles Times. “I hoped I was hitting a lot of people with it.”
Cui uses a laptop computer and a video projector powered by a portable generator to cast his images on blank walls.
[…]
“What he put up is the equivalent to an advertising sign and not a work of art,” said Dave Keim, head of code enforcement for the Department of Building and Safety. “To us, anything that attracts the attention of the public is a ‘sign’ and you need a permit.”