You can add custom tracking campaigns to obtain a specific referrer for each tracking. This is useful to keep track of the provenience of a specific visitor. For example, if you are sending newsletters or marketing emails to your customers, you can include such instructions in the links and track who clicked on them and then searched for a car. The same function can be used to track other kind of marketing campaigns, such as ones from social networks or analytics techniques used by search engines. To set up a custom campaign rule you need to specify a request key (make sure to not use preserved request keys, numbers are always better), optionally a request value fort the key, and the name of the campaign that will be used as referrer for the trackings.