As used in this part, “equity security” means any stock or similar security, or any security convertible, with or without consideration, into a stock or similar security, or carrying a warrant or right to subscribe or to purchase a stock or similar security; or a warrant or right; or any other security that the commissioner deems to be of similar nature and considers necessary or appropriate, by rules and regulations the commissioner prescribes in the public interest or for the protection of investors, to treat as an equity security.