Okla. Stat. tit. 69 § 655
The board of county commissioners in each county may, within one (1) year after the designation of the county primary road system in that county, locate, erect and thereafter maintain markers designating those routes classified as county primary roads. Markers shall bear the cardinal number or other identification assigned the particular route on which the marker is erected and shall indicate the name of the county. The responsibility for devising a practical, systematic county primary route numbering scheme, including the configuration of the identifying device, readily lending itself to functional implementation is vested and imposed jointly on representatives of the Oklahoma Cooperative Circuit Engineering Districts Board and the Department of Transportation. The scheme shall be so devised as to offer intracounty and intercounty road users a convenient means of identifying and using the county primary road system and shall provide for continuous numbering of routes crossing county boundaries. The Department of Transportation is hereby authorized to negotiate with the counties, on a statewide basis, to manufacture and provide the markers on a materials plus cost basis.
Okla. Stat. tit. 69, § 655