Denial of one religious group’s rights to advertise would be a government interference in their religion.
My understanding of the First Amendment is that government isn’t supposed to get involved with actively promoting any sort of religious message.
Hence, the prohibition of tax dollars going to religious schools in the USA.
However, not everyone out there always follows the law, so some transportation authorities may advertise messages with religious slogans, as Dale mentioned in Iowa.
There is a slick argument and loophole that atheism is not a religion, so the secularists and atheists use that argument and to brainwash their opponents, even though atheism expresses a direct opinion involving the existence of a Deity / Creator (God or Gods), and nullifies the basis of almost all religions.
Also, sometimes you have to fight legally instead of caving in to the multiculturalist liberals every time they threaten a lawsuit.
There are a few Christian based legal services non-profits like the Thomas More Society and the Alliance Defense Fund that may take the case for free or at a reduced cost.
That’s what that school district in Mississippi did; they stood their ground and didn’t cave in to the lesbian student who wanted to dress like a boy and attend the prom with her girlfriend or to the ACLU.
At least the federal judge didn’t force the school to accommodate this person this school year.
That Mississipi school district at least has some gumption, and earned my respect, even though they lost the case because of some liberal multiculturalist (i.e.,many cultures) federal judge’s opinion.