First thing that comes to mind ... assuming that you have been installing vmware-tools on the VMs (which is recommended), you can check if /usr/bin/vmware-toolbox exists.
The other option would be to use the "dmidecode" command which converts the system DMI into readable format. So in essence when you run
Code:
dmidecode | grep -i vmware
you should be able to tell if your system is a VM or runs on hardware.
HTH