We do not have code available for a pop up form; however you can get the embed code for a sign up form. If you are looking for something with more functionality like popping up, I would recommend checking out the Marketplace for an Application that might help or a partner who might be able to code something for you.
Thank you for your response. From what I can tell the "embed HTML" does pop up. The standard HTML only shows a submit button. It would be nice to have a regular form too that can be added to "about us" etc.
I don't follow you, you asked for a pop up window.
The link can be text as well as the button you see.
Here is an example that we did for a client.
When you get to the page click on the button that the arrow points to.