You cant write a message, it should be a picture. And it wouldnt work on anybody from a forum signature.
Those type of things work because like...When you are at a movie, you always have the urge to buy a drink or popcorn or a snack. Now your eyes capture the image, but it goes by to fast for you to actually recognize it was shown. However, your brain still gets the message and it says "Coca Cola" so you think of Coca Cola and you realise you want a Coca Cola. Its more effective if done several times so the person continuesly thinks/wants a Coca Cola and then finish it off by having actors enjoy a Cola in the movie. My friends mom is a phsyciatrist and his science projects always involve stuff like this. He uses us as expirements, its pretty cool