I looked at the different strings used by Steam Guard and the only relevant ones I've found are when there is reasonable doubt that your account has been compromised. This is an example I actually got when I logged onto Steam on my laptop:
Here's the other alternative:
Since you last logged in from this computer, your account credentials were used and Steam Guard was disabled from another place.
Please confirm these sessions were authorized by you:
If any listed sessions were not authorized by you, select 'No, this was not me' to change your Steam password and email address, deauthorize other locations and re-enable Steam Guard.
Both dialogues are referenced by this published FAQ article on Steam Guard Notification.
Just to be complete, if you want to deauthorize the all other systems you have previously used, you can go to the settings in the menu, press the "Manage Steam Guard account security" button and check the "Deauthorize all other computers now" checkmark before pressing next.