Fallout: New Vegas locations project
The billboard in front of the church displays the Bible verse "REVELATION 9:6", which according to one translation is "During those days people will seek death but will not find it; they will long to die, but death will elude them." This is in reference to the ghoulified NCR soldiers and the quest We Will All Go Together.
The billboard used to read "BINGO EVERY TUESDAY NIGHT 6:30 9:30", which would account for why the "L" in "REVELATION" is actually an upside down "T".
The Searchlight church appears only in Fallout: New Vegas.