On https://meta.wikimedia.org/wiki/Special:MyLanguage/Requests_for_comment/Password_policy_for_users_with_certain_advanced_permissions it was suggested by User:°, that the instructions for creating an account/changing password, should instruct users to use a unique password, and not share across multiple websites.
So in order to make this really useful, it should be a label element with a for attr in order for screen reader users to be clearly connected to the element.
See for example https://doc.wikimedia.org/oojs-ui/master/demos/?page=layouts&theme=wikimediaui&direction=ltr&platform=desktop#FieldLayout-aligned-top-with-inlined-help
This is also the correct styling of additional, secondary labels. Note the white-space connecting it visually to the first and related password input and not to the second.