As used in sections 38a-118 to 38a-124, inclusive, “equity security” 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 to purchase such a security, or any such warrant or right, or any other security which the Insurance Commissioner shall deem to be of similar nature and consider necessary or appropriate, by such regulations as he may prescribe in the public interest or for the protection of investors, to treat as an equity security.