If the content of your Plone site is not editable by the general public, there is no point in displaying the login link to non-authenticated users.
Remove Login Action
- Plone: User Login Action
To remove the login button,
- go to Site Setup → Zope Management Interface
- navigate to portal_actions/user
- edit the login action
- untick the Visible? check box
While this will hide the login facility from the visiting public, the personal tools menu will still remain accessible for the logged-in user.
Those who need access to the site, can simply bookmark the site's /login page.
Hide the Personal Bar
Alternatively, if you don't want to delve into the ZMI, you can hide the personal bar via the viewlet manager at /portal_actions/@@manage-viewlets.
- Plone: Manage Viewlets
However, this has the disadvantage that it will also affect authenticated users as links to Dashboard, Preferences and Site Setup will no longer be conveniently accessible from the personal tools drop-down menu.