We simply use dry erase markers and draw on all our windows. The boss's office has two glass walls that look out onto our Video Network Center, we painted (on the inside) one set with white latex paint cause he didn't want everybody able to see into his office and those get the 'long-term engineering plan' type drawings. The other windows we also cover in marker, but typically more day-to-day or short-term project oriented (such as "Chris is no longer allowed to speak when the Div. Chief is in the room!" etc.

At a previous job, back before flat screen TV's became ubiquitous we had probably 25 or so 27"-40" CRT monitors to display conferences on. We used dry erase markers to label the sites/conferences/start-end times, etc. when things got hectic. We also would, on occasion, use markers to add comic-style speech balloons with inspirational quotes for customers that were less than, um... friendly.

Let's just say that we were glad that all our monitors faced away from the hallway windows and nobody but Ops personnel were allowed in our VNC.