Sigma Nesterowitz
Sigma Nesterowitz was a star system in the Alpha or Beta Quadrant.
In 2367, Sigma Nesterowitz's position was labeled on a tactical situation monitor in Captain Benjamin Maxwell's ready room on the USS Phoenix. (TNG: "The Wounded", okudagram)
In 2366, in an alternate timeline, during the Federation-Klingon War, Sigma Nesterowitz's position was labeled on a tactical situation monitor on the bridge and in the ready room of the USS Enterprise-D. (TNG: "Yesterday's Enterprise", okudagram)
Appendices
Background information
This star system was only mentioned in writing.
It can't be deduced from the star chart in which quadrant Sigma Nesterowitz was located as there were planets and star systems from both quadrants spread throughout the chart.
In the Bayer designation, which was a system of stellar classification, the Greek letter indicated the brightness of a star in a constellation. In this case, Sigma Nesterowitz would be the 18th brightest star in its constellation.
It was named after craft service John Nesterowicz.