OT: which display is active

[Robert Arkiletian]

I need a little help.
Assume there are two or more people logged in to separate X sessions
with "Switch User" on the same box (not LTSP).  If I ssh in to that
box (as root), how can I tell which display is the active one?
Put another way, is there any way to tell which display is currently
being shown.

-- 
Robert Arkiletian
Eric Hamber Secondary, Vancouver, Canada