Σ
Symbol  Format  Data 

Σ  Code Point 
U+03A3 
TeX 
\Sigma 

SVG 
The capital Greek letter is visually very similar to the summation symbol (∑) which is the dedicated symbol in math for the summation operation.
In math, the summation symbol (∑) is used to denote the summation operation, which is a way of expressing the addition of a sequence of terms.
The Greek letter σ (sigma) is used in statistics to represent the standard deviation of a population.