When in Thailand, do that you see the locals doing.
When the National Anthem of Thailand is played, you MUST stand up and still!
The Thai National Anthem, Sansoen Phra Barami, is played twice a day in Thailand, at 8:00 AM and at 6:00 PM.
Also, if you are in a movie theater and the National Anthem plays, stand up with the rest of the Thai Patrons in the movie Theater.
If you do NOT stand still, and you get reported but the Thai’s, you will get yourself in a world of legal trouble.
Show respect ALWAYS!