One of the things I like to do when the NCAA and NBA are in their off-seasons is "go retro" and examine historical court designs. Before the Milwaukee Bucks moved in 1988 to their current home, the Bradley Center, they played in what is now known as U.S. Cellular Arena and was previously known as Milwaukee Arena and the MECCA. Toward the end of the Bucks' time at the MECCA, the bulding sported an unusual floor design -- dreamed up by pop artist Robert Indiana -- that used different shades of shellac to create a giant "M" on either side of the half-court line (see image below, which I took from here). In case you've wondered what happened to the double-M floor, the answer is here.
Even before Robert Indiana's contribution, however, the Milwaukee Arena/MECCA featured another unusual floor element, a dotted (not dashed) line semi-circle in the keys (above right; from the video “Oscar Robertson best skilled player ever,” available on YouTube).