Revisiting the Macie console after leaving it running for a month or so, I see the locations from which my account has been accessed. As it happens, these are the locations I have been working in recently.
From the docs:
AWS CloudTrail provides you with a history of AWS API calls for your account, including API calls made using the AWS Management Console, the AWS SDKs, the command line tools, and higher-level AWS services. AWS CloudTrail also enables you to identify which users and accounts called AWS APIs for services that support CloudTrail, the source IP address that the calls were made from, and when the calls occurred.