You can track Segments on both Accounts and Contacts. The example below is on the Contact, however the same applies to the Account. If you haven't already set up the field, settings and Segments required, please see this article.
Changing the Segment selected in the monitored field, in this example called 'Segment', will result in a Segment History record being created in the Related List.
The Start date will be set to today, the Segment recorded, and if there was already a segment previously selected, the old Segment record will be marked as 'Former'. You can click the 'View All' link to see all the details logged.
In this view you can see which segment is current and which were former.