There's a standard for everything. Really. Quality Digest's ever vigilant editors came across this relatively new one from ANSI. By the time this horse is tricked out with lights and signs its going to look like the Borg.
--Editor

From an ANSI news release:

Seeing a horse and a buggy can evoke romantic memories, but the merging of high-powered vehicles with animal drawn equipment in urban centers or on public roadways creates potentially hazardous situations requiring special safety procedures.

A recent standard, ANSI/ASAE EP576.1 JUL2008—"Lighting and Marking of Animal Drawn Equipment," from the American Society of Agricultural and Biological Engineers (ASABE) establishes a unique identification system for slow-moving animal-drawn vehicles, such as Amish buggies, horse-drawn farm wagons, and urban carriages on public roadways or highways.

The document includes proper lighting and marking of both the vehicle and the animal, including the use of headlamps, tail lamps, battery-operated or generator-powered lighting systems, and retroreflective material, as well as rules on the display of slow-moving emblems. This identification system is intended as a complement to existing laws, rules, and regulations in individual states, provinces, and municipalities.

An accredited standards developer and organizational member of the American National Standards Institute (ANSI), ASABE is an educational and scientific membership organization of agricultural, food and biological engineers seeking to develop efficient and environmentally sensitive methods of producing food, fiber, timber, and renewable energy sources.