Go to ITouchMap and enter the address. You can drag the arrow to the exact part of the building your classroom is in if you are in a super huge building.
This site will give you decimal coordinates. You can convert them to degrees, minutes, and seconds using the Federal Communications Commissions site.
Then you just spend 30 minutes unwinding, playing with your favorite fonts and color combinations and work up something like this. Goes great with the north, south, east, and west labels we all have in our classrooms. If anyone from my school wants a copy of the "real deal", email me and I'll send you a copy. I don't love the idea of putting my exact coordinates on the interweb! Ha!
Of course I got the inspiration for my sign from Pinterest!