Subliminal messages are very much prevalent in the world of advertising. These are messages which are presented below the threshold of human understanding. The chances of they being understood by humans is lesser than 25%. The technique is to give inputs below the threshold of conscious perception. To illustrate, consider a advertisement that flashes in front of you on TV or cinema, but is so short and fast that your conscious mind does not acknowledge it. It comes in every form of media from print to web, packaging, logos and magazines to movies. You could say that it’s graphic design at its best.
So, yes, subliminal messages are not a fiction, they are real and existent.
The question here is: How often do we encounter them?
http://www.wordofmouthexperiment.com/articles/subliminal-messages/subliminal-messages-marketing-fact-or-fake
Subliminal messages are everywhere and sometimes we don’t even noticed them. We see them when we eat, when we see a movie, read a magazine article and in many other forms. This messages are any stimuli below the individual’s threshold for conscious perception. Many companies used them including: Camel, Swensen`s ice cream and even Disney. There are a couple of videos you should check out regarding subliminal messages:
https://www.youtube.com/watch?v=cHuC-ev7fQ8
http://library.thinkquest.org/07aug/01592/images/ad2.jpg
https://www.youtube.com/watch?v=73fCLx-mFLg
It is amazing how a company such as Disney, in which their market is children, still uses subliminal messages in their movies. So I agree with you, subliminal message is a fact and it happens in the real world and still does.