Probably it can't be turned off. You can only search on "Mature" section manually. For example, this member Dorogochi, has several (or even all) mods with mature contents in them & if you visit the profile, you'll see empty profile. But if you search manually on "Mature" section from page 10, you can see the mature mods by Dorogochi.

Actually it would be better to make it so that the sensitive contents can be turned on & off by clicking that notification as long as the option for "Mature Contents" is enabled, because that would make the items easier to search than manually checking the "Mature" section. But well, it's up to the admin & staff whether to implement it or not.