Oh God, I've been seeing far too many of those stupid "I'm a Mormon" ads too, they're on YouTube now. What is the point of them?
proselytize
v.intr.
1. To induce someone to convert to one's own religious faith.
2. To induce someone to join one's own political party or to espouse one's doctrine.
v.tr.
To convert (a person) from one belief, doctrine, cause, or faith to another.
Duh.
As a government entity they have to accept all religious advertisers or none of them - are you that unfamiliar with the standards by which a secular government has to be run?