Automatically record the site URL which contains my stateless iframe embedded form

Automatically record the site URL which contains my stateless iframe embedded form

Hi not sure if possible but lets see

I have 20 Sites each with the same contact form (name, email phone etc ..)
I am using a stateless form embedded in an iframe

The only difference in the form is that i hard code in a hidden field the url of the website, this is so i can determine which website sent the user submission

So at the moment i have 20 forms.

Would be nice to cut it down to one form, if only i could write some script that would allow me to determine which site the form is on and have that value stored in creator upon submission

I don't mind putting something on the server as an ID nor do i mind modifying the template (wordpress and joomla)

Any ideas ?

Thanks in advance