Anchor link helper

I want a way to pop up my subscription form. It uses a #code in the URL so that they stay on the same page. But you require that the link be a full URL, and I have no idea whatever what page they're on. E.g., if they're on domain.com/sale the code would be domain.com/sale#code. By requiring a full URL you force a page change, which slows things down dramatically.