In Xp and Vista it was easy to retrieve the display device ID (I.E. \\.\Display1, \\.\Display2, etc). The returned deviced ID's matched the display numbers as depicted on screens with the "identify" button....where a big '1' and '2' would appear on the monitors if clicked.
In Windows 7, this...
bug report
display identification
display numbers
enumdisplaydevices
getmonitorinfo
graphics
graphics card
hardware
hardware id
multi-monitor
random
reliability
resolution
tech support
troubleshooting
user issues
windows 7
windows vista
