What DBus signal is sent on system suspend?

Your question led me to something that works here:

> annotate-output dbus-monitor --system "type='signal',interface='org.freedesktop.UPower'"
08:07:00 I: Started dbus-monitor --system type='signal',interface='org.freedesktop.UPower'
08:07:00 O: signal sender=org.freedesktop.DBus -> dest=:1.145 serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameAcquired
08:07:00 O: string ":1.145"
08:07:22 O: signal sender=:1.20 -> dest=(null destination) serial=189 path=/org/freedesktop/UPower; interface=org.freedesktop.UPower; member=Sleeping
08:07:41 O: signal sender=:1.20 -> dest=(null destination) serial=190 path=/org/freedesktop/UPower; interface=org.freedesktop.UPower; member=Resuming
08:08:10 O: signal sender=:1.20 -> dest=(null destination) serial=192 path=/org/freedesktop/UPower; interface=org.freedesktop.UPower; member=Sleeping
08:10:08 O: signal sender=:1.20 -> dest=(null destination) serial=193 path=/org/freedesktop/UPower; interface=org.freedesktop.UPower; member=Resuming

So as you can see I did get the signals you seem to be missing. @08:07:22 I suspended the machine, @08:07:41 I started it again. @08:08:10 I hibernated it, and @08:10:08 it was restarted again. Works flawlessly here. I did try adding ,member='Sleeping' like in your post, and that worked too (only gave me the Sleeping events).

BTW, I really like annotate-output

Under Fedora14 I use the same command dbus-monitor --system "type='signal',interface='org.freedesktop.UPower'" can monitor the signal with suspend signal. Check your UPower Config.