tedster - 11:27 pm on Sep 28, 2008 (gmt 0)

What are they a sign of?

I mentioned something about that in the second post - they're a navigational aid for the end user. Google assigns Sitelinks algorithmically for some queries, based on traffic, website architecture, and some other "special sauce" ingredients. Sitelinks began at first for only the strongest domains, and that may have caused some confusion. As they became widespread, it became clear that having Sitelinks for the basic query [domain.com] was not all that special any more.

Now, if you see Sitelinks for a generic keyword query, rather than a full domain "navigational query", then that might show something about authority - but it still isn't about trust.