Within your control panel, you can track several metrics to determine how well individual forms are performing within your account. You'll find these reports in two sections in your account: the "Sign Up Forms" section and the "Reports" section.
Sign Up Forms
If you go to the Sign Up Forms section of your control panel, you'll see a table with several columns, with some that report statistics about the effectiveness of each form.
If you hover over the heading of each column, you'll find an explanation of those statistics. The descriptions for each column read as followed.
Displays the type of sign up form: pop-over, pop-up, lightbox, and inline (embedded into the webpage like a standard form).
The number of times this sign up form has been displayed to website visitors.
The number of subscribers who have signed up thru this sign up form.
The ratio of subscribers divided by unique visitors. Shows your unique conversion rate.
If you go to the Reports section of your control panel, you'll find all of the different reporting that is available for your email campaign.
Under the Ad Tracking - Subscribed section of your reports, you will find a table that shows how many times someone has subscribed to your list. Each ad tracking value will be attributed to the subscriber both as a raw number and a percentage of the whole.
This figure helps you to determine which forms are performing best on your site, and in order to use it, you will need to have set an ad tracking value for each form in the campaign you are working in.