WordPress at a glance
action is not described

signup_blogform action-hook . WP 3.0.0

Fires after the site sign-up form.

Usage

add_action( 'signup_blogform', 'action_function_name_8211' );
function action_function_name_8211( $errors ){
	// action...
}
$errors(WP_Error)
A WP_Error object possibly containing 'blogname' or 'blog_title' errors.

Where the hook is called

show_blog_form()
wp-signup.php 197
do_action( 'signup_blogform', $errors );

Where the hook is used (in WP core)

Does not used.