Register, Trademark and Copyright Symbols
http://www.itcfonts.com/Ulc/2811/RTC.htm

Strizver, Ilene
Upper and lowercase Magazine
2002

Abstract:

Register, trademark and copyright symbols are important communicators. They help establish brand identities and protect creative work from theft or plagiarism. Despite their legal and symbolic power, these symbols need to speak softly, typographically speaking. Their tasteful and appropriate use is a small but significant part of good typography.