The current pavement sign marking operations are manually carried out, which are labor-intensive. This method requires blocking traffic for a long period of time resulting serious traffic jam. Also, the workers are exposed to possible injury and even death by passing traffic. This paper deals with the development of a robotic system for automating the pavement sign painting operations. The robotic system consists of gantry frame equipped with omni-directional wheels and paint spray system. The workspace of the gantry robot is extended to one-lane width with the omni-directional wheels that are attached to the corners of the gantry frame. This research also includes the development of font data structures that contain the shape information of pavement signs. The end-effector path is automatically generated with this font data through the procedures of scaling up/down and partitioning the corresponding signs depending on the workspace size. The robotic sign painting equipment and related control algorithms are built and tested with real painting experiments of various signs, which shows satisfactory results.