Anti-Copyright. (usually a © symbol with a red slash through it. see Suvertise.org for a picture )
The idea is that when the author or creator of some intellectual property places an anticopyright on it instead of a copyright (©), then the object becomes a member of the public domain for use as you see fit, thereby giving it up to everyone, but requiring that it remain under the anticopyright. (meaning the only restriction is that it remain in the public domain)
for example of use, see discrimination