No branding

Pro

A paid feature: part of Pro, or of upgrading a single form. See Plans & pricing.

What visitors see on a free form

Under the form, a card: "Made with Fill Out This Form", a line about what it is, and a Make your own form button to our home page.
After they send their response, under the thanks, an invitation to make a survey of their own.

Removing it

With Pro, it's gone from all your shared forms.
Upgrading a single form removes it from that form's links.
There's nothing to switch on: it disappears as soon as the form is paid for.