Source

File: wp-includes/ms-functions.php

function is_user_spammy( $user = null ) {
	if ( ! ( $user instanceof WP_User ) ) {
		if ( $user ) {
			$user = get_user_by( 'login', $user );
		} else {
			$user = wp_get_current_user();
		}
	}

	return $user && isset( $user->spam ) && 1 == $user->spam;
}