The device for measuring the current or emf is connected within the circuit of the thermocouple. It measures the amount of emf flowing through the circuit due to the two junctions of the two dissimilar metals maintained at different temperatures. In figure 2 the two junctions of the thermocouple and the device used for measurement of emf (potentiometer) are shown.
I think that this is what advertisers are shooting for when they pay the big price to get their ads up there. Regular billboards are just as effective as ever, even though there are now digital billboards being made that can have multiple ads on them and switch between them every few seconds.
According to the book Creative Advertising by Charles Whittier:  A slogan should be a statement of such merit about a product or service that is worthy of continuous repetitive advertising; is worthwhile for the public to remember; and is phrased in such a way that the public is likely to remember it.