How is the frontend header's «Sign In» link rendered?

Layout

Default layout

The default Magento_Customer module’s layout places the «Sign In» link (with the internal name authorization-link) inside the top.links block:

Luma theme

The Magento 2 default design theme (Luma) creates another «Sign In» link (with the internal name authorization-link-login) and places it inside the header.links block:

Then, the Luma design theme moves the top.links block inside the customer block:

So, the original «Sign In» link (with the internal name authorization-link) is not visible because the customer block is visible only to the authenticated visitors:

Also, the Luma design theme contains an odd nonsense move instruction:

It has no sense, because the authorization-link is already inside the top.links block, as it defined in the the default Magento_Customer module’s layout:

Template

See also:

• How is the frontend header’s «Create an Account» link rendered?
• How is the «My Wish List» link rendered in a customer’s dropdown menu in the Luma’s header?
• How to modify the \Magento\Customer\Block\Account\AuthorizationLink::getLabel() method («Sign In» / «Sign Out» text)?