Caught Peeing at the Crime Scene

I was taking a wiz at the urinal closest to an open window overlooking the forensics lab's crime scene when one of the students, pointing to the bathroom window said, "Hey, there's an open window there."

The lab assistant, spotting me, said, "And there he is." I waved with my free hand, wondered if this was similar to the Paris pissoirs: guys relieving themselves while people looked down from their offices.

There was a difference: I was above rather than below the crowd. In the time I had to reflect, I wondered whether I should wave? If so, with one hand or two? What was the proper look to have on one's face while relieving oneself? Impassive? Joyful? Relieved? Studious? (Will a survey reveal a gender-based difference in responses?)