Cached signatures

Hi, we are using Adobe Sign for Dynamics 365. We recently sent an agreement to a customer where the customer was using a generic email address. The recipient forwarded the email to a colleague and when the colleague opened the agreement to sign it they were prompted to with a further colleages signature, depite never having used Adobe Sign previously themselves. 

Why was the colleague prompted with another users details? Are signatures cached on some way with the email address?

Thanks