Marking your project as 'Mature' can be done during the creation of your project, or edited within the personalize tab if you've already created the project with mature content.
Initial Setup of Mature Content
In order to mark your project as 'Mature', be sure to check "My project contains (18+) Mature Content" before clicking 'Create Project'.
For existing projects planning on releasing mature content, navigate to the personalize tab (the paintbrush icon on the left navigation in your content dashboard) and open the Project Branding Settings Page. Scroll to the bottom of this page and check the box marked "My project contains 18+ Mature Content"
For more information, be sure to read our content policy outlining Mature Content Guidelines and Enforcement.