Or if you just want to see the link quality one time:
Or if you want to see the link quality continuously, you can use:
watch -n 1 cat /proc/net/wireless
Or if you want a continuously running graphical plot of the link quality of all signals available:
I use wavemon quite a bit since it is ncurses based (It runs from the terminal screen) so you don't need to start up the gui.
My Raspberry Pi Project Page: