Global function in file auto_prepend.php:

/**
 * Check if a text entry for a specific label exists
 * @param $label Label to check
 * @return label name if text exists in current (or supplied) language, false otherwise.
 */
function T_exists($label, $language = null)
{
    it_text::init();
    return $GLOBALS['it_text']->text_exists($label, $language);
}