Oh, how times have changed. Back in the dinosaur days (c. 1972), when I was in school learning proper business usage, I was taught that one never signs one's name with a title, whether that title is M.B.A., J.D., Esquire, Ph.D., or M.D. It was considered in poor taste and never was to be done. Nowadays, I see all these letters after people's names and most of the time, I don't even know what they mean. People sign themselves "John Smith, Esquire," and I was taught that was tantamount to blowing one's own horn and was greatly frowned upon.
My professional organization is constantly trying to get members to sign up for its "certified manager" designation. Costs thousands of dollars, so there's the reason IMHO. I can do my job just fine without it.