In the good old, bad old days, before computers were omnipresent, designers used to spend hours rubbing away at transfer sheets of letters. Letraset was the brand leader but we are really talking about dry transfer type. The Letraset company still exists and continues to sell its transfer sheets. It was founded in 1959, at which point mechanical artists (I mean people creating mechanicals for printing, not guys drawing car engines) heaved a sigh of relief. They no longer had to send out to a jobbing typesetter to get type set for their mechanicals; they could just pick up a sheet of Letraset from their local art supply store and apply it directly to their boards.
The sheet carrying the transfer type had a bit of tack to it, so it wouldn’t slip about, and came with a protective backing sheet of tissue paper. As you can see from the picture there was a dashed alignment guidance system below every letter. Like the guy in the picture, most people didn’t really use this. We weren’t “setting” Letraset for long paragraphs of type: just for the title and author on a book jacket, say. You’d rub off the letter using a pencil, or a special rubbing tool, lift away the carrier sheet and burnish the letter by placing the tissue paper backing sheet over the line of type and rubbing a smooth-sided object back and forth over it until the letters were well and truly bonded to the board. Although they wouldn’t just fall off the letters remained fragile — you could easily damage them by failing to pay attention, and of course mechanicals were always themselves protected by a covering layer of thin paper.