There is more than one type of “subliminal” advertising. Not all of it is unlawful.
Since the 1950s it has been illegal in the United States to make television commercials in which images are “flashed” on screen so rapidly that the conscious mind is not likely to perceive them. It was in 1973, I believe, that the promoters of a children’s game called “Husker Du?” ran afoul of this ban by flashing “get it” on screen several times during a commercial.
The technique is also illegal when used as James Vicary claimed to, by flashing an image on the screen while a movie is being screened in a theater. There is, however, no universal ban on using subliminal images on film or video. Examples of movies with such images include Psycho, The Exorcist and JFK.
In some prints of the film Psycho, during the long, slow close-up on Anthony Perkins towards the close of the movie, the image of a withered corpse shown earlier in the film is briefly superimposed on his face. (I could be more specific about what is shown and what it symbolizes, but there is always the outside chance that there is someone out there who still does not know about the “surprise” ending of the movie.)
In The Exorcist there are at least three shots of a demonic-looking face which last about two frames each. It is arguable to what degree these are truly subliminal. Some people are said to be wholly unable to remember having seen them. I recall seeing two of them clearly when I first saw the movie. They appear during Fr. Karras’ nightmare, and later, during the exorcism as Karras looks at Regan tied down in bed. When the movie was rereleased a couple of years ago I saw it again, and was surprised to see a third shot. It comes relatively early in the film, when Regan is being examined in a hospital.
In JFK there is a shot lasting exactly one frame. During a scene at a party at the home of Ferry (Joe Pesci) a shot of a dangling skeleton is jammed between two longer shots.
So far as I know, there is no similar restriction on subliminal advertising in print media, where the technologies used are far different, and a ban would be far harder to frame or enforce. One difficulty is that it is hard to define just what counts as submliminal in a still image; there are all sorts of innuendoes, double entendres, and symbolic references in the print media which would be hard to ban without severely restricting free speech.