To call yourself an engineer you need an Engineering degree from a qualified institution (4 or 5 years), at least 2 years of apprenticeship (effectively), and to pass a difficult examination.
They're not typically huge fans of people who haven't done those things calling themselves "sanitation engineers" or "software engineers" instead of "janitors" and "programmers". The argument I usually hear is that it undermines their profession; people can hold the work of an engineer to a particular standard. If suddenly I can say "oh, I'm a software engineer" without anything backing that up, it damages the reputation of "engineer" if I behave poorly.