OK :D
you have to find this symbol.
http://www.shineon.in.th/wp-content/uploads/2012/10/%E0%B8%AD%E0%B8%B2%E0%B8%AB%E0%B8%B2%E0%B8%A3%E0%B9%80%E0%B8%88-4.jpg
there's many Thai peoples that're vegetarian.
there's many vegetarian restaurants in Thailand. Thai people call "Ran J" and you can buy vegetarian food in 7-11 that some 7-11 have a vegetarian food for you.
or there's cooked to order restaurant.
you can choose in menu but you have to tell them about you are vegetarian.
สัญลักษณ์