Determine if x is running

[redhat at buglecreek.com]

I'm am writing a script that sets some various security settings on
Redhat Boxes.  I would like to try to determine if a gui may be running
on the box the script is run on.  If so, I would echo some additional
text to stdout that instructs the user that they may required to
manually perform some additional settings manually.  Things having to do
with screen savers.  Anyway, I thought about the following:

1. use the runlevel command or who -r to see if the system is in
runlevel 5.  This seems flawed since the box may have been started in
runlevel 3 and the startx command may have been used. The commands would
show runlevel 3.
2. Check if the environment variable DISPLAY is set.  If so, seems like
there is a good chance that they are running a gui. (maybe)

Is there a better way to check this that anyone can think of?