Get one of the mowers that follows a wire and then embed the wire under the grass in the pattern you want.
I remember seeing one of these where a guy would mow outside a pattern at one height, then adjust the height of the mower and mow the inside of the pattern so the grass was longer, giving him a noticeable pattern. Can't find a link at the moment though.
No. I often mow my lawn in a pattern to produce nice stripes. It's also commonly done on sports stadium grass. A pattern (if chosen for efficiency) can actually reduce the wear of riding/pushing a lawn mower over the grass by minimizing the number of passes needed over a given patch of grass.
I remember seeing one of these where a guy would mow outside a pattern at one height, then adjust the height of the mower and mow the inside of the pattern so the grass was longer, giving him a noticeable pattern. Can't find a link at the moment though.