A Maryland Route 223 route marker, own work. Made according to http://www.marylandroads.com/businesswithsha/bizstdsspecs/desmanualstdpub/publicationsonline/oots/pdf/M1-5.pdf using Inkscape.

This file is in the public domain because it comes from the Maryland Manual on Uniform Traffic Control Devices, sign number M1-5, which states specifically in its introduction, on page iii that: Any traffic control device design or application provision contained in this Manual shall be considered to be in the public domain. Traffic control devices contained in this Manual shall not be protected by a patent, trademark, or copyright, except for the Interstate Shield and any items owned by FHWA.