How to identify where a lead comes from and attribute it to a lead source?

[Anita_Singh6]

I need to be able to know where a lead is coming from and add it to our lead source. Our lead source can't be based on when it's fully known to us because we have a lot of places that a lead could be coming from whether it's a referral page, paid search, organic search, or direct. When it comes to referrals or organic search we don't have the ability to add a query string to that URL. So, I need to know of another way to be able to source where that lead comes from. 

How can I do this?

Thank you,

Anita

[Vladislav_Vagn1]

This thread might give you some more information on what you are looking for:

https://nation.marketo.com/thread/31499