It's pretty accurate to say that Muay Thai has no belts.
As pointed out, there are some gyms and organizations that do grant ranks. However, it's not really accepted at all in the general Muay Thai community. Saying that Muay Thai has belts is like saying BJJ has several belts in between white and blue. There are a couple of BJJ gyms that do award belts in this way, but it is uncommon and not at all generally accepted by the BJJ community.
Thai people will look at you like you are crazy if you claim a black belt in their art.
As pointed out, there are some gyms and organizations that do grant ranks. However, it's not really accepted at all in the general Muay Thai community. Saying that Muay Thai has belts is like saying BJJ has several belts in between white and blue. There are a couple of BJJ gyms that do award belts in this way, but it is uncommon and not at all generally accepted by the BJJ community.
Thai people will look at you like you are crazy if you claim a black belt in their art.