TimeStamp
The following Applescript allows me to mark a mounted external (eject-able) disk with a time-stamp. This is done by touching a "CCC.timstamp" file or folder at the root level of the disk, which causes the current date/time to be recorded as the Modification DateTime.
If the file of folder doesn't exist, an empty file is created. The Applescript displays a dialog box with the names of all mounted disks, and three buttons: the name of the first disk, Cancel, and Next. If you click Next, then another dialog box appears showing the name of the second disk as the first button, and so forth until you either click on the diskname button, or Cancel, or run out of names clicking Next. If you click the diskname button, that disk's CCC.timestamp is time-stamped.
I've attached the Applescript. Just download it, double-click it to enter the Script Editor, Compile it, then "Save As..." to save it wherever you like. Then use "Save As..." again and select "application" from the "File Format" list, choose just the "Run Only" option, Hide Extension, and select a place to save it (I usually put it on my Desktop).
Click the "Save" button, and you now have an application that will time-stamp your eject-able disks. This was originally written for CCC (Carbon Copy Cloner), but should work with any backup software.
I've also attached an Eject.applescript that you download, compile in Script Editor, and save as an "application" wherever it is convenient for you. This application will eject all mountable volumes, including mounted disk images from .dmg files.
Both of these scripts ignore the bootDisk, "Network", and "afs".