Sigma, officially the Municipality of Sigma, is a 4th class municipality in the province of Capiz, Philippines. According to the 2020 census, it has …Sigma, officially the Municipality of Sigma, is a 4th class municipality in the province of Capiz, Philippines. According to the 2020 census, it has a population of 31,688 people. Sigma is 28 kilometres from Roxas City, the provincial capital.