This website contains age-restricted materials including nudity and explicit depictions of sexual activity.
By entering, you affirm that you are at least 18 years of age or the age of majority in the jurisdiction you are accessing the website from and you consent to viewing sexually explicit content.
That’d be about as ridiculous as the proposal that is being dismissed into oblivion in this thread but at least economically and technically feasible.
Three or four signs should suffice.