Is it really any of your business how someone signs into this forum??
Do you mean the admins of the forum? Yes, yes it is.
I found it odd when I saw it on other lists, but when I compare it to other lists where people have "handles" or just their names on their comments, anonymity and in-group identification fall under the idea of the Greater Internet F#%kwad Theory.?
When you ask people to make themselves clearly known, they know accountability is possible, and they TEND to behave more civilly. I've run mailing lists and other forums since dial-up bulletin boards back in the 80's and before. Anonymity (or lack of clear identity in the forum's in-group) breeds abrasive behavior. In ham radio groups, what identifies you as part of the in-group is your call sign. And yes, they have a perfect right to demand it. Some lists won't even approve you for membership if you don't have a call sign. Heck, just look at CB radio! At least in the US, 11-meter CB is comparable to a Mad Max movie. Some people on 75-meters ignore the identification rules, and where they do, it's a Caprican Cluster-frak.
So...yeah, requiring members on the list to supply a call sign at some point is a useful civilization tool. The more rigid groups require it when you ask for admittance. The more easygoing just ask you to either put it in your name field so it's in the header, or in your signature block. I use the latter, because it's easier to remove if I'm sending an email to a non-ham. (I could set up a custom "From" identity in Gmail, but it's not what I like to do.)
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(Some of this has been a little tongue in cheek in terms of delivery style, but the concepts remain apt. Please forgive me, Hans.)
Gwen Patton