Road signs in Thailand are rather similar to the ones used in western countries, but some signs are also specific and a few of them are also written in Thai only. That’s why we always advise long term residents to learn not only to speak Thai, but also to read and write it. All direction signs, though, are bilingual (Thai and English).
Did you know? In 1968, in an effort to facilitate international road traffic and standardise traffic signs, the European countries, as well as India and a few other countries, signed the Vienna Convention on Road Signs and Signals treaty. It is interesting to note that Thailand signed the treaty, but did not ratify it.