When using multiple monitors from the same brand and size, its currently a guess which monitor is which in the combobox. This patch adds some more detail by using the EDID 0xFC product name descriptor as display_name if 0xFC contains the vendor name, e.g. 'DELL P2414H' instead of 'Dell 24"'. Otherwise 0xFC is added in brackets to the default display_name, e.g. 'Samsung 21" (SyncMaster)' instead of just 'Samsung 21"'. If 0xFC is empty the old display_name is used.
Created attachment 6951 Patch to include 0xFC product name in combobox
Created attachment 6952 Patch to include 0xFC product name in combobox
Not sure this really helps, especially if you have two displays from the same maker/brand/model. To uniquely identify which display is selected we implemented the "identification popups".
Unfortunately those identification popups are almost useless and only add to the confusion which screen is what in some cases. I have had an issue with X that assumes the primary display is at 0,0 (which it isnt in my setup, its in the middle), so when I run a fullscreen program (eg the screensaver) and come back from that it puts the main screen always at 0,0 causing two screens to overlap. As they overlap, you cant select them both graphically in xfce-display-settings and you have to use the dropdown, but if it says three times (Dell Inc. 24") you just dont know what is what. And as the identification popups also uses that overlapping screen configuration, you cannot use that either because it will just show eg 'Screen 2' on both screens (the number depends on your exact config, but it will show only one number the other is invisible because those identification popups also overlap)
Btw, that was a reply to both this issue as 13286 to show the identification popups are not always working so another solution to clarify which screen is what would be helpful