County and Route RA in Lee's Summit, Missouri. Combinations beginning with the letter R are also used for routes that connect with state parks or other recreational facilities, which is the only use of R on the system; Route AR, a non-recreational route south of Bakersfield, is the only exception to this. The vast majority of the highways in the system are designated with 19 letters of the alphabet. The letters "G", "I", "L", "Q", and "S" are not used because of the potential confusion with other letters and numbers. The only current use of X is on Route AX in Macon County. Supplemental routes rarely run for more than a few miles, although they may cross county lines. A route's designation changes at a U.S. Route or Interstate highway; for example, in Greene County, southbound Route J crosses U.S. Route 60 and becomes Route NN, and Route M in Cole County becomes Route J after passing U.S. Route 50. However, when Route MM in Greene County crosses Route 360, it remains Route MM, only changing to Route B when crossing Interstate 44. Route J in Boone County is one of the few exceptions to this, as it continues past U.S. 40 for three miles before becoming Route O upon passing I-70. Designations are also reused, but not near one another. For example, Route D exists in the counties of Cole, Greene, Newton, St. Louis, and several others. Rarely is a designation reused in a county; exceptions include two highways designated Route Z in Randolph County and two highways designated Route K in Carter County. In some cases, supplemental routes will share a concurrency with a state route or another supplemental route. For example, Route J in Howard County overlaps with Route 87 for about near Boonesboro, Route D in Greene County overlaps with Route 125 for a few miles, Route N and Route O in Franklin County overlap for between Catawissa and Robertsville, and Route CC in Moniteau County overlaps with Route C for a few miles. Signage Supplemental routes are signed by black letters on a white background with a black border. Rarely, the shields will be marked with banners such as EAST, WEST, or END. There are no business or bypass routes for the roads; however, seven examples exist of spur routes: Spur Route N in Cedar County, Spur Route C in Gentry County, Spur Route C