I love that particular series of pennants, and know that they were issued in/around 1951. I have one with a written notation on the reverse, which states the date of the game and the teams who played (July, 1951). These pennants could've been sold for a few subsequent years, of course.
There is also a nifty series of Lapel Pins with these identical team logos. These pins are apparently (interestingly) dated 1954...
http://www.ebay.com/itm/1954-Basebal...IAAOSwll1Wz3Mb