If you do

ssh -L 5432:localhost:5432 yourpc.example.com -l username

And you want to see the active tunnels following this comment from superuser.com

From within an ssh session:

1. press enter
2. type ~ and then #

shows you a list of all open connections over your tunnels for that session.

Note: This will only show the client connection and active tunnels meaning that you have something connected and passing traffic through the tunnel.