"Sisters of Mercy house of prostitution" joke

A man is driving down a deserted highway, and notices a sign that reads: SISTERS OF MERCY HOUSE OF PROSTITUTION - 10 MILES He thinks it was a figment of his imagination - and drives on.
Soon, he sees another sign which says :SISTERS OF MERCY HOUSE OF PROSTITUTION - 5 MILES Realizing these signs are for real, he drives on, and sure enough, there is a third: SISTERS OF MERCY HOUSE OF PROSTITUTION - NEXT RIGHT
His curiosity gets the best of him, and he pulls into the driveway.
On the far side of the parking lot, is a somber stone building with a sign on the door that reads: SISTERS OF MERCY
He climbs the steps, rings the bell, and the door is answered by a nun in a long black habit, who asks, "What may we do for you my son?"
"I saw your signs along the highway, and was interested in possibly doing some business."
"Very well, my son. Please follow me," says the nun.
He is led through many winding passages, and soon he is very disoriented.
The nun stops at a closed door and tells the man, "Please, knock on this door" and leaves.
The man does as he is told, and this door is opened by another nun in a long black habit, holding a tin cup. This nun instructs: "Please place $50.00 in the cup, then go through the large wooden door at the end of this hallway." He places the money in this nun's tin cup.
He trots eagerly down the hallway, and slips through the door, pulling it shut. As the door locks behind him, he finds himself back in the parking lot, facing another small sign: "Go in Peace. You have just been screwed by the Sisters of Mercy."