AFS Analytics can display different design of buttons on your website pages (visible or invisible). You can change the design in selecting the option "Button displayed on your website" into the form "Edit website info". Top menu -> Account -> Edit website info or Manage websites option. Here is a help video that covers this feature.
The Invisible button is limited to the first 50,000 page views per month. Once the limit is reached, a small AFS logo will be displayed on your website pages. This does not affect tracking or analytics reports. You can increase this limit by upgrading your account to silver or gold plans.