Korush'nai is a Goa'uld symbol of warning. Loosely translated, it means "turn back," and is used to indicate any planet destroyed by the Goa'uld and left contaminated by radiation. SG-1 encountered the ominous warning on P3R-233, a deserted world that had been destroyed by the Goa'uld.
Cross Reference: Destroyers, Goa'uld Language, P3R-233
Episode Reference: There But For the Grace of God