The most common pose for Buddha images in Thailand is the seated image displaying the Bhumisparsha Mudra gesture, more commonly known as the "subduing Mara" pose.
A Buddha Image from Sukhothai, one of the earliest Thai kingdoms.
Mara is a demon who attempted to lure the meditating Buddha away from the path of enlightenment. The story goes that the Buddha was meditating on his way to attaining enlightenment when Mara came to try and force or tempt him from the spiritual path - this was, in effect, Mara's "job". Mara assaulted Siddhartha Gautama with memories of his life back in his palace; his armies of lust, desire, hunger and thirst; and even attempted to lure the young man with his lovely daughters. In a way, Mara is the embodiment of that feeling of self-doubt which is present inside of all of us.
But the former prince was having none of it. He extended the fingers of his right hand towards the ground and summoned the earth goddess Toranee to bear witness and help defend him from the attack. The goddess wrung her long hair, releasing a torrent of water that washed away Mara and his army.
Some Buddha images in this pose also have a small statue of Toranee placed beneath them.