In education, it's imperative that you'd have your credentials on your CV. If they take the form of letters after your name, then fine. You would, for instance put Post Graduate Certificate in Education (PGCE) to prove you'd taken a post-graduate course and enhanced your skills as an education professional. Many schools and colleges will look more favourably on any candidate who has a PGCE. However, you wouldn't add it to your email signature when working at a school or college because everyone around you probably has one and it would simply be superfluous. However, let's say you left education and wanted to work for a theatre company doing outreach work in schools/colleges, etc and other workshop settings with children and young people. A PGCE on your CV is going to look better than even a BA (Hons) on its own (which many candidates will probably have in the same interview room). It's not a professional body membership acronym or even a qualification (though it is) in many ways - for certain contents it is not just a badge that says you learned about Shakespeare in your BA (Hons), but that you understand how to teach Shakespeare within a formal pedagogical framework. Those with a PGCE are prized, so you'd be remiss to exclude it when applying for certain jobs.
I've never once thought anyone with letters after their name is a prat. If you're proud of things you've achieved then great. Especially where the thing you've achieved moves you to a new stepping stone in your career, rather than just means you've kept your membership of something up to date.
I do have a problem with titles given by royalty as these are applied for, not necessarily earned directly. This is open to abuse ... Titles for Cash....just nominate someone for an award and get cash in your pocket in return.