I do believe that there are ads that try to 'manipulate' us and make us associate certain feelings or things with different products. I also believe that there are some people who look too far into things and start to see messages that no one intended to exist.
The kind of liminal advertising that I believe is created by the advertisers and the designers are small design things or when an ad is seen. For example the FedEx logo
it's a logo that people see very frequently and has a small design element that most people never notice until someone points it out to them. In between the E and x an arrow is created in the whitespace. This is liminal advertising. It imbeds an idea in the viewers mind that with FedEx your package will go wherever it needs to go (as the arrow implies movement of some sort).
When or where an ad is viewed can also imply liminal advertising. If someone is looking through an expensive magazine and they see an ad for a certain brand of shampoo they're going to immediately relate this product to also being expensive and high class (even if it's the same as any other shampoo). It's also seen in television. Companies will buy ad space during certain programs depending on the content. If a show is happy then companies who want people to associate happiness and feeling good to their product will buy ad space during that program.