Using credentials in private email signature

How appropriate is it to use one's degree credentials when signing an email to a friend/acquaintance? I know a couple of people who do and I just hate it. How do American-born see this? I've been in this country for over two decades and think I'm quite assimilated but I can't get my mind around this. A degree credential seems to be used like an aristocratic title would (or used to) in other places. I don't see the relevance of reminding the people you know what college degree you've got. Of course, I'm not talking about business email, where that would be completely appropriate and even necessary. I'm talking about personal chat between people who have a strictly personal relation. What is the purpose of stating the degree credential? Is it to say, "this is who I am -- I'm fully identified with my job/career"? Or is it to say, "I am just so proud of myself that I can't help reminding you of what I've accomplished"? Or is it begging, "Value me. I deserve it"? To me, it puts the email recipient in a position of competition, as if told, "I show you what I've got; now you show me what you've got." Now, where I'm from we don't show off degree credentials. We know they have little to do with the real value of people. My degree credentials are the result of following a specific course of study at an accredited institution. Big deal! Who cares besides me? I still don't understand what people in the US (can this be made a generalization?) think of themselves for having a degree, particularly what they think of themselves in respect to other people. People who get a PhD love to call themselves "doctors." How could that be relevant outside of the job except in the aristocratic sense of expecting to be treated as superior?