The other day I saw a subliminal advertising executive, but just for a second. - Steven Wright
There's two kinds of subliminal advertising. One is when an image is deliberately planted - for example, watch for the woman in bra and panties in the lower right corner halfway through this ad.
The other is when something is supposed to be implied by the use of imagery. Such as the horse running free in the surf in this one.
Or did you see something else?