Interesting you mentioned Woodie Guthrie. For many of his songs published after a certain time, legend has it that the copyright notices went something like this:
"This song is Copyrighted in U.S., under Seal of Copyright # 154085, for a period of 28 years, and anybody caught singin it without our permission, will be mighty good friends of ourn, cause we don't give a dern. Publish it. Write it. Sing it. Swing to it. Yodel it. We wrote it, that's all we wanted to do."
I wouldn't count on something like this if I was using his stuff but, damn, that guy was extremely cool.