The Indian prince who became the Buddha after seeking salvation meditating under the Bodhi tree, Siddhartha Gautama was not portrayed by portraits or sculptures for several hundred years after his death with regard to his teachings. (He explicitly requested not to create depictions of him as his message was conveyed as a man, not a deity that was the most significant part of his teachings). Find additional information at https://www.yourbuddhastore.com/collections/buddha-statues/
Sometimes he was symbolized by a circle reflecting the ‘Dhamma’ or the circle of life that proceeds to spin or his foot symbolizes his journeys where he transmitted the word of non-attachment and enlightenment.
Eventually though he was a focus for artists and craftsmen to seek to reflect his identity as his word spread and his power circulated across the ancient Eastern world. The most famous image to be seen today is that of a sitting Buddha where he is peacefully meditating in a lotus pose. Of course most of us have seen many Buddha picture renditions that show him in a number of other ways, for example: the standing stance, the reclining stance, or even even a walking pose that sometimes holds a bowl with an alm.
Therefore, the significance of the sitting meditating image of the Buddha is that there are various descriptions, movements, mudras and positions that the Buddha can have and that amount can exceed several hundreds or even thousands. Each gesture means something different, and is crafted or sculpted according to long-standing traditions that vary from country to country.
Any of these variants may be: earth touching mudra, yoga pose, golden robes, “urna”—or a hair topknot (popular in Thailand and SE Asia), carrying an alms cup, sitting on the bed, etc.
In my experience the sitting Buddha signifies probably the most peaceful and quiet positions of all Buddha positions. In doing so, I personally think he looks so relaxed, calm but erect in his seated posture. If we find ourselves sitting in a similar position after meditation and feel our spine straight and upright while our shoulders, hands, arms, torso, face are relaxed then we mimic the common seated posture of the Buddha. It was my understanding that I first needed to lean against a settee or wall before the sitting / meditative pose was good enough for my body structure. Then the next phase was to find out how to keep my mind still which is of course the most difficult task of all and one where it can certainly help to look at the serene image of a large seated Buddha in meditation.