A couple of ways - on the main WIS page, you can put your mouse over the link to your team, and you should see the "tid =xxxxx" in the lower left corner of your browser. The same information is available if you put your mouse of the team name at the top of each page (it looks like "javascript:OpenTeamProfile(55346,0);" - the 55346 is my Princeton team in Yost.
Or, you can use this chart I made a long time ago and forgot about until just recently.