Lately I see this message when a new member has placed his/her first post:
This is the first time xxxxxxxx has posted — let’s welcome them to our community!
What I think is a bit strange is the way the new member is addressed, namely with the word them.
Wouldn't it be better to change that text a little and say, for example:
This is the first time xxxxxxxx has posted — let’s welcome this new member to our community!
Also, when it is possible to show this text, it is also possible to add a link to the thread where is explained how to write a decent post, with lots of information about the issue:
Two flies with one stone.