"Sisters of Angelica" joke

A man is driving down a deserted highway when he notices a sign that reads...
SISTERS OF ANGELICA HOUSE OF PROSTITUTION 10 MILES
Thinking it must be a figment of his imagination, he drives on without giving it a second thought. Soon, he sees a second sign which reads...
SISTERS OF ANGELICA HOUSE OF PROSTITUTION 5 MILES
Now realizing that these signs are for real, he drives on and passes a third sign...
SISTERS OF ANGELICA HOUSE OF PROSTITUTION NEXT LEFT
Curiousity getting the best of him, he pulls into the driveway. Beside the parking lot is a sombre stone building with a sign on the door that reads SISTERS OF ANGELICA. He climbs the stairs, rings the bell, and the door is answered by a nun in a long, black habit. "What may we do for you, my son?" she asks.
"I noticed your signs along the highway and am interested in possibly doing some business," he replies. "Very well," says the nun. "Follow me."
She leads him through many winding passages and he soon becomes quite disoriented. She then stops at a closed door and tells him, "Please knock on this door," and leaves. He knocks and this door is answered by another nun in a long, black habit, holdng a tin cup. Please place $50 in the cup, then go through the large wooden door at the end of this hallway," she instructs. He places the money in the cup, continues eagerly down the hall and slips through the door.
As the door closes and locks behind him, he finds himself back in the parking lot, facing another small sign which reads...
GO IN PEACE
YOU HAVE JUST BEEN SCREWED BY THE SISTERS OF ANGELICA