When you register, you are asked for both a USERNAME as well as a DISPLAYNAME. You will always be quoted by your @username.
The USERNAME has to be unique — while DISPLAYNAME does not need to be unique.
For simplicity, you may want to use THE SAME NAME for both fields – the DISPLAYNAME is the one shown everywhere throughout the site.
You can always change your DISPLAYNAME later in the profile edit – you CAN NOT change your USERNAME.
On a Side Note: Registration Moderation
As of September 29th, 2015, we are moderating all membership registrations – rather than going through them after the fact to check if a spammer tries to sneak in via automated scripts, all new registrations are now held in a queue until manually approved. The admins receive emails and on-screen alerts of pending registrations, so it should not introduce any significant delays. But it should guarantee a spam-free environment on Scaffies.
After registration and subsequent activation (by a link automatically sent to the registered e-mail address), the new member gets this message (also in email). Once approved, a second email follows informing the new member he is now ready to go. Until the approval is made, the new member is very restricting in what he can do, but he can continue to update his profile.