Not the US. If I open any link to a pin or try to browse a list, I get this: https://i.imgur.com/MQUoa2N.png

Note the lack of an [X] button. This popup is both modal and non-dismissable, so you can't even click on links to other unauth areas. For non-technical users, the literal only options are signing up or closing the tab.

It's not really a secret either. They wrote detailed posts on their tech blog about both the invention of the non-dismissable modal popup [1] and the descision to make the image the user was looking for less obvious compared to recommended content [2].

[1] https://medium.com/@Pinterest_Engineering/lessons-in-growth-... [2] https://medium.com/@Pinterest_Engineering/lessons-in-growth-...