The Cadillac Series 61 Touring Sedan is a 4-Door class vehicle available in L.A. Noire. It is identifiable as a 1947 model, matching the convertible version also available in the game.
Sometimes one is parked on Sunset Boulevard in a driveway between Orange Dr. and La Brea Ave. in Hollywood
Have been spotted around the intersection of Catalina and 5th in Wilshire (Catalina runs north to south and runs between the large L and S)
One is sometimes parked in the parking lot right across the road from the police station in The Red Lipstick Murder.
There may also be one parked behind the building you use to sneak up on the sniper in Manifest Destiny. The address of the building is 1384 North Bronson Avenue, and it's just south of the intersection with Fernwood Ave on the western side of the road.
Also sometimes found on corner of Selma Ave. and Vine St. in Hollywood. It has also been found just before the corner of 1st Street and Normandie Avenue by a bus stop. On the map, this is where the right V of the letter W in Wilshire cuts across the road.