I know that σ is the symbol typically used for standard deviation, but what does the use of σ mean in these contexts? ex. 1: "[our fancy new instrument] ... allows for the identification of > 500 sources at greater than 10-sigma" ex. 2: "These estimates assume ... a 1σ polarization uncertainty P = 1%. Please note that if the symbol doesn't show up for you, it is supposed to be the letter sigma.