wp-includes/ms-functions.php:2158Adds a nonce field to the signup page.
function signup_nonce_fields() { $id = mt_rand(); echo "<input type='hidden' name='signup_form_id' value='{$id}' />"; wp_nonce_field( 'signup_form_' . $id, '_signup_form', false );}Introduced in MU (3.0.0). Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/ms-functions.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.