Gather source material. Images of Thai artwork are readily available from libraries and online. The traditional art of Thailand has characteristics that may be adaptable to the purposes of a Thai restaurant. Gather examples of sculpture, architecture, woodworking and painting from all periods of Thailand's art history.
Make sketches. Base your sketches on your source material. Making many sketches can help generate ideas and make you familiar with the visual style of Thai art. Make note of the use of color in traditional Thai artwork. Adapting the colors and shapes used in traditional Thai art may help relate your design to the culture of Thailand. Experiment with color combinations using some form of color media, such as markers, colored pencils, pastels or watercolors.
Refine your ideas. After making numerous sketches begin to focus on just a few drawings. If you appropriate an image or symbol for your design make sure you fully understand what it represents. Consider the ways in which the information of your sign can be conveyed most clearly. Once you have decided on a final design, make a full color, scale drawing based on the dimensions of the finished sign.