My Salesman Data Book dated 1/15/1952 on page 14 Sec 8 shows a locking cap, it looks like this one but without the wings. It also appears in the 1951 Salesman Data Book on page 210: Did not see it listed in the 1947,1948,1949,or the 1954 (I do not have a 1953 book).
http://good-times.webshots.com/photo/2753248720102454676wtHBlpThis is the text describing it and they are shown with two keys that have GAS clearly visible on them.
Prevents theft of gasoline, as well as refilling without the keys. Reduces the possibility of gasoline dilution. Thwarts loss of gas tank cap, as keys cannot be removed unless the cap is securely locked. The spring snap-down cap prevents rain, sleet and dirt from entering the lock.
