SIGMA was an electronic verification service offered by Nielsen Media Research, generally used to track airplay for commercials, infomercials, video news releases, public service announcements, satellite media tours, and electronic press kits. The video tracking service operated by encoding a SIGMA encoder ID, alongside the date and time of encoding, into lines 20 and 22 of the analog video signal. This placement was within the vertical blanking interval, outside of the area displayed on a standard television screen (similar to how analog closed captioning was transmitted). On a professional video monitor with underscan capability activated, or on a computer display of the entire video frame, the SIGMA data appeared as small, moving white lines at the top of the frame. Using this data, Nielsen provided overnight reports of airplay across television markets. With the global transition to digital broadcasting, traditional analog encoding became largely obsolete as the industry shifted to digital watermarking technologies. In March 2026, Nielsen formally announced the termination of its decades-old SIGMA Radio monitoring service, delivering its final reports in April 2026 and concluding the remaining services in the SIGMA tracking suite.
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