Effectiveness of subliminal messaging (i.e. visual and audible signals which are so quick/quiet/subtle that they're available only to your unconscious mind) is not that hard to test in a laboratory, and studies are pretty conclusive that it it doesn't influence decisions unless the stimulus is presented within a few seconds of making the decision (i.e. grocery store aisle).

People are definitely swayed by overt, liminal signals in subtle ways, but subliminal messaging specifically was created by an ad agency and the science was pretty well debunked.