Ann, There are 3 'generations' of the PT 140. The 1st gen. had frame cracking problems...double action only. The 2nd gen. was a newer model, the PT140 Millenium Pro (with the cracking problem resolved). On the left side of the slide is printed 'Millenium Pro', on the right side, PT140. This is also double action only.
For the 3rd generation, the newest model (3rd series), The PT 140 Millenium Pro is DA/SA (both double and single action). On the left side of the slide appears, "Millenium" and on the right side of the slide-"PT140 Pro".
To date the gun for when it was made: Look at the 1st three letters of your serial number. Your 1st letter should be an "S"....meaning .40 cal. Your 2nd letter could be V-2002, W-2003, X-2004, Y-2005, and Z-2006. Your 3rd letter would be an A through L, representing the month it was manufactured....Jan to Dec.
To see if you have the newest model, just look at the 2nd letter of your serial number....if it's a "Z", it's the newest model.