Bring your own writing stick to sign the log in this geocache.
The name CN89nc is this location's grid square on the Maidenhead or locator grid. The locator grid is used by ham radio operators and others to quickly get an approximate location in a shorthand way using Morse code or some other communication method. In addition to ham radio, I find that it's useful for sending in weather reports with my location, but in a way not so specific to invade my privacy.
For more details on the locator grid, see the relevant Wikipedia article: https://en.wikipedia.org/wiki/Maidenhead_Locator_System
Also see this interactive map of the locator grid: https://f5len.org/tools/locator/