The first thing one reads is FOR SALE, because of its height, its large bold sans serif font, and its bright orange and yellow background; at the same time, one probably at least senses the rather run down warehouse-like building on which it is hung. Then one reads the lower, smaller font, white lettered DERMATOLOGISTS, and (perhaps having been told this is supposed to be a joke) reblends to combine the two signs into one; one may also notice the small "Now selling" sign below. It is the blending that creates the humor, creating the incongruous idea of selling doctors. Strictly speaking, this is not an oxymoron, because the effect cannot be obtained from just the words without the visual setting.