Membership "Sign Up" button url

I would like to use a pricing table on my subscriptions page instead of the usual membership subscription listings. For the button in the pricing table I need a url for the "Sign Up" button so that it will show the membership "subscribe" popup when people click the button at the bottom of the pricing table.

Is there a url for this popup or a way to add it to a pricing table so people can get a good side-by-side comparison?