Okla. Stat. tit. 47, § 47-12-213: Lamps, reflectors, and flags on projecting load

A. Whenever the load upon any vehicle extends to the rear four

(4) feet or more beyond the bed or body of such vehicle, there shall

be displayed at the extreme rear end of the load, at the time

specified in subsection B of Section 12-201 of this title:

1. Two red lights and two red reflectors positioned to indicate

maximum width; and

2. One red light facing to each side positioned to indicate

maximum overhang.

The required lights and reflectors may be mounted in combination

at each side of the vehicle and shall be visible from a distance of

one thousand (1,000) feet.

B. At any other time on any such vehicle, there shall be

displayed at the extreme rear end of such load red flags not less

than twelve (12) inches square marking the extremities of such load

at each point where a lamp would otherwise be required by this

section.