One of our Text building blocks used to say:
Welcome to tex.sx! Note that it is unusual to have any greeting.
to put as a comment under questions which start "Dear all,". To me this comment sounds like
Hello. Don't say hello.
Two discussion points came up to me:
Although I think we should encourage users to write clean questions, we also want to make them feel welcome, and I wonder if having their first feedback from the community be a reprimand for their use of a simple greeting accomplishes that.
The word "unusual" strikes me as underscoring the newbie's newbieness, since they obviously don't know what's usual.
I edited that block to say
Welcome to tex.sx! It's not necessary to sign your questions (as there is already a box with your username below it) or to begin them with a greeting.
but it could still use some work. I left out "Note that" since it doesn't make any difference in the sentence and only serves to make the writer sound/seem important.
"Customary" might be a better replacement for "usual", although "uncustomary" doesn't really have the right connotation either. Perhaps it's better to say "It's customary around here to do X instead of Y" rather than "It's unusual/uncustomary to do Y".
I know not all users (questioners and answerers) are native English users, so please don't take offense with my nitpicks over word choices. But I might be tweaking the building blocks more to improve the effect they're designed for.