Final answer:
The standard deviation is represented by the Greek letter sigma, with the lowercase sigma (σ) denoting population standard deviation.
Step-by-step explanation:
The standard deviation in notation is represented by the Greek letter sigma (o for population standard deviation and s for sample standard deviation). The notation symbol for population standard deviation is lowercase sigma (σ), not to be confused with the capital sigma (Σ) used for summation or the other listed symbols. Therefore, the correct option for the appearance of the population standard deviation in notation from the choices given would be 'o with a line over the top' which is essentially attempting to describe 'o' the lowercase sigma. It's important to note that the correct visual representation of sigma is without the line over the top, and it closely resembles the English letter 'o'.