The term "equity security" when used in this act 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 director of the department of insurance shall deem to be of similar nature and consider necessary or appropriate, by such rules and regulations as he may prescribe in the public interest or for the protection of investors, to treat as an equity security.