What do we call encircled letters?

Question

you know like encircled C for copyright, T for trademark.. is there a word for those letters? please?

Answer 1

You may not want the correct answer to your question, but I shall offer it nevertheless.  

The encircled "R" is an OFFICIAL SYMBOL.  Standing for "Registration" (in the USA with the U.S. Patent and Trademark Office; internationally by the World Intellectual Property Organization, under the Madrid Protocol) it is indicated by an encircled "R" following the name or logo.

The encircled "TM" (or "SM" in the case of service marks) is an UNOFFICIAL SYMBOL or DESIGNATION which tells others that you claim common law rights in the mark. The encircled "TM" may also be interpreted to mean that you have applied for federal registration, and are awaiting a decision.

The only other designation for encircled letters of which I am aware is that used by Microsoft Word:  Special Character.  I believe that this designation is idiosyncratic and not an appropriate substitute for "Official Symbol," "Unofficial Symbol," or "Unofficial Designation."