After much consideration............
I would suggest one or more of the following above your ass crack:

"Exit Only"
"Authorized Personal Only"
"Over a billion Served"
"Go Where Angles Dare Not Tread"
"Beware all Yee Who Enter"
"BOMBS AWAY!"
"USDA CHOICE"
"Would you like Fries with that Shake?"
Golden Arches
A picture of George Bush
The words from the Star Spangled Banner (to be taken out on special occasions only)
A picture of Pope Benedict
The words to the Battle Hymn of the Republic.
A list of all major past and present Evangelicals in the US, with a slash through the names of the dead ones.
A tattoo of a butt with a tattoo butt.