I'm sure this is a simple thing to do but.. I'm trying to make a wireless link indicator on the outside of the casing for a routerboard. I'm using RB433UL boards. I'd like to have a way to see if a link is made and if the link can pass traffic. I'm not familiar with the commands for printing the wireless stats but I figure that's a good place to start. Any ideas? 

Use some network management system like dude for example and graphs the values obtained via snmp.

Look up user LEDs in the manual there are five you can program. They can be used for antenna alignment (signal to noise)
and activity etc.
http://wiki.mikrotik.com/wiki/Manual:System/LEDS

There are clear plastic tubes called lightpipes to get the LEDs to show outside the case.
http://www.mouser.com/new/vcc/vccflx/