Indiana Code Title 9. Motor Vehicles § 9-21-9-4

Sec. 4. When a slow moving vehicle described in section 1 of this chapter is moved, operated, or driven on a highway at a time or under circumstances during which the use of lighted lamps on vehicles is required under this article, the slow moving vehicle must display, in addition to the slow moving vehicle emblem, a red or an amber flashing lamp mounted at a height as low as practicable that is visible from a distance of not less than five hundred (500) feet to the rear.  The red or amber flashing lamp may be used at times other than when lighted lamps are required.  A double-faced flashing lamp may be used, displaying amber light to the front and red or amber light to the rear.