> What led you to ask about aliases?
I saw comments elsewhere in this topic. Hadn't crossed my mind before that.
> Are there people you communicate with regularly
> refer to by their alias?
If I suspect the person might not want to be called by their username (maybe they don't hate it enough to change it or abandon the account, but prefer their displayname), I'll try to respect that. If it's someone I don't know well, I could be guessing wrong. Only one comes to mind, but I don't want to make an example of them here.
> Are there other people you see doing this?
It can be noticeable when they don't. E.g. If a comment is signed "Guy" and the next commenter mentions "JzG", any reader who is unfamiliar with the way he signs will do a double-take, and eventually may hover (or long-press) the names to discover that they link to the same user page. It's unusual for the alias and username to lack an obvious connection, but it does happen.
Can't say I've really noticed how often people do pipe the user link. It might be possible to do some automated analysis to quantify this. I suspect unpiped is more common, but could be waaay off-base there.
I see people like WhatamIdoing, Iridescent, and GorillaWarfare referred to as WAID (sometimes), Iri, and GW (often), but usually in plain text and not as part of the ping. (See next.)
> Something else?
Sometimes I'll risk being overly-familiar and manually pipe a shorter version than the display and user names. Maybe initials for a really long name, or something like [[User:john.q.citizen|John]] for someone who uses what looks like a real name. That's probably not a common practice, and isn't changed by the search-and-insert function.
> Have you read any documentation that talks about what the "correct" way is ...?
No, I wish I had.
> If you're not familiar with MediaWiki, then you would probably try to ping someone by the displayed name instead of the real username.
Yes. In the current method of replying, I start a section-edit and can see the previous users' sigs in their wikitext forms. I can copy-paste a user-page-name directly, with its User: prefix; and, if it's unstyled, the piped displayname also. But if a user is replying in a discrete box, the displayname/alias is the thing they see on-page, and they need to know about hovering or long-pressing a link to see the URL, then discern the username from that.