I'm a ringed engineer; I think it's appropriate for non-ringed engineers to still self-identify by that title. An engineer is a person who engineers things.

There's a legal restriction on Professional Engineer and the P.Eng designation, but that's for very good reasons which have to do with liability and the protection of the public. That's a different beast, though, and in the general case "engineering" a solution to a problem is still engineering, whether or not you have a piece of paper telling you it is.