The term “equity security” when used in this chapter means any stock or similar security or any security convertible, with or without consideration, into such a security or carrying any warrant or right to subscribe to or purchase such a security, or any such warrant or right, or any other security which the Commissioner deems to be of similar nature and considers necessary or appropriate, by such rules and regulations as the Commissioner may prescribe in the public interest or for the protection of investors, to treat as an equity security.