As a non profit why lock away your contributions to society with a threat to litigate? Easy Way Blocking Knitted Things At Home
All copyright does is allow you to sue someone if your work is used by someone else.
Non-profits should tag their work with a Creative Commons license that allows other to build on the work and add to the NPO community as a whole.
I strongly recommend removing copyright notices in favor of an attribution only license which allows other to build on your contributions to the community as long as they credit the author. Most NPO’s want their work distributed in ways that help as many people as possible. All a copyright notice does is discourage sharing with the community as a whole.