Many Vegan travellers and tourists in Thailand ask me about this.
Save it into your phone and show it everywhere you order food. You can also look out for it in shops and on packets in 7-11 and other convenience stores.
Its not actually a "symbol", its simply a word, 2 letters if you like.
The letter on the left makes the sound of "ay". The letter on the right makes the sound of "je".
In this case, the "ay" vowel sound is situated in front of the "je" part - the wonders of Thai Language. Lets not get into all that right now!
Please note, its not a literal translation of "Vegan". The Thai word "jay" is a little more complicated, which I will share more detail about in another blog. But just for now know that Thai People who eat Jay also dont eat certain things like onion and garlic, so your food may taste a little bland! But, if you want to be safe on your vegan travels, just show the restaurant / shop owners this sign.