Erwin Moller wrote:
>>>> after the user left the site and
>>>> returned.

> I think you are wrong. ;-)
> Or I miss something completely in this discussion.
>

Part refer is useful, is the moment when user *returns*.
Not when he's leaving. I believe that Sebastian wants to detect
*returning* clients (so he wont display welcome to them), not leaving ones.

If Sebastian sees that the users was on his site recently (session is
already there), but the refer does not point to his site, then he can
guess, that the user was on a site X and from the site X returned to his
site.

Ofc, you need to assume that session is stored in cookies, users accepts
and keep them, and that he returns by clicking on link.
But as for such trivial thing, as hiding welcome message, you can do so,
without risking it will spoil browsing experience for anyone.

best regards
Piotr N