if I have several sources of various web forms and need to know what form is the lead, where did it come from?, how can i know the form source?

if I have several sources of various web forms and need to know what form is the lead, where did it come from?, how can i know the form source?

if I have several sources of various web forms and need to know what form is the recorded lead from?, how can i know the source? 

in my customization i used "applicants" as leads. thank you