Reattaching to an existing screen session

Reattaching to an existing screen session

I have a program running under screen. In fact, when I detach from the session and check netstat, I can see the program is still running (which is what I want):
udp        0      0 127.0.0.1:1720          0.0.0.0:*                           3759/ruby      
Now I want to reattach to the session running that process. So I start up a new terminal, and type screen -r
$ screen -r
There are several suitable screens on:
    5169.pts-2.teamviggy    (05/31/2013 09:30:28 PM)    (Detached)
    4872.pts-2.teamviggy    (05/31/2013 09:25:30 PM)    (Detached)
    4572.pts-2.teamviggy    (05/31/2013 09:07:17 PM)    (Detached)
    4073.pts-2.teamviggy    (05/31/2013 08:50:54 PM)    (Detached)
    3600.pts-2.teamviggy    (05/31/2013 08:40:14 PM)    (Detached)
Type "screen [-d] -r [pid.]tty.host" to resume one of them.
But how do I know which one is the session running that process I created?
Now one of the documents I came across said:
"When you're using a window, type C-a A to give it a name. This name will be used in the window listing, and will help you remember what you're doing in each window when you start using a lot of windows."
The thing is when I am in a new screen session, I try to press control+a A and nothing happens.