Original version appearing on wikimedia commons
A symbol meaning "not-copyrighted"
This symbol consists of the letter "C" inside a circle with a line through it.
The letter C inside a circle generally means "copyrighted."
A circle with a line through it generally means "do not participate in whatever action is depicted inside the circle."
c
Circle with line through it, conveying meaning "do not"
line slanted from lower left to upper right signifying negation