Mathematics today owes its existence to the discovery of zero. For the purpose of calculation, it needed a short symbol. India for ages has denoted this number 'sunya' by both a dot (.) and a small circle (o). Let's look back at the journey of this magic number- the number that represents absence when placed independently, and fullness when placed among other numbers!
Sunya has many references in the vedic literature. May it be the Amarkosa, Ganita Sastraka or the Atharvaveda- sunya is present. Sunya also finds its references in the Bakshali Manuscript (200 AD), the Shahpur stone inscription (672 AD) of Adityasena, Bihar and the Malay inscription of Katakapur (686 AD). Zero in all of these inscriptions, manuscripts and scriptures is represented by either a zero or a dot.
The obvious question that may arise is why is zero represented by either a dot or by a small circle? Why not by a square of a triangle? The answer has both metaphysical and physical aspects. In the spiritual sphere, sunya identifies with the conception of Brahma, both in absence (nirguna Brahma) and fullness. The conception of Brahma further lies in meditation on a particular point or circle. Therefore the symbol of sunya!
In the physical aspect sunya gets its symbol from planets that look like dots. According to Vedanga Jyotisa (1200 BC), the concept of the astronomical space is similar to that of the paramanu or molecule (Lalita Vistara, 500 BC). This book not only correctly gives the diameter of an atom, but also goes on to claim that that the molecule has both the aspects of absence and fullness, similar to that of sunya!