Url or title to form response mail

Hi.

I have one form that I use for subscribing to multiple categories in events. So people will have a signing up form.

How can I show the url or page title on the form, so that the admin can tell on witch event was the user subscribing to?

I tried to pass a variable into template, but I guess this doesn't work for forms?

<?php $actual_link = "https://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]"; ?>

<?php PerchSystem::set_var('actual_link', $actual_link);?>