Well it depends on what kind of site it is. For my own event sites, I maintain a privacy and disclosure policy, a republishing policy, and some method of contact - be it email address or a contact form. I'm not selling anything on those sites, and they're all pretty well marked with my extensive and unique (cough cough) social footprint, and it doesn't seem to have been an issue so far.

For my ecommerce clients - most of my clients are B2B in old and established niches, and the toll free number does seem to make a difference (we've tested it) My biggest client has a call center in order to offer 24/7 phone orders and customer service, and so far none of his competition (apart from the super huge players like Amazon) do that - that gets used quite a bit.

I think the ecommerce security signals do make a difference, particularly on sites that deal with banking or financial niches.

I believe strongly in a robust About Us page for professional organizations or ecommerce, with physical addresses, staff and management names, pictures, and as much specific information as possible. For Google purposes, tying to a local business profile (Google+) probably means something (not to users so much, but to Google)

I try and put revolving testimonials on site if I have them. And I mean testimonials about the company, not just the products.

I was recently contacted for consulting by a company that was offering ... not exactly medical advice, but something just bordering on the edge of it. The first thing I noticed was that there were NO professional credentials on the site whatsoever. In other words, there was no reason for me to believe these people knew what they were talking about. If you're in a field like that - or basically any field where you're setting yourself up as some kind of expert or authority, you better say WHY you're an expert, and hopefully provide some kind of third party confirmation to back it up. Things like certifications, awards, membership in industry organizations.

I'm sure there are more, have to think about it.

Might be a good place to link to the Stanford Web Credibility Project [credibility.stanford.edu] in particular, this top 10 list [credibility.stanford.edu]

It's not up to date or by any means comprehensive, but I've found it a good reference point in terms of what Google might be aiming to achieve.

Toll Free Number* - Does this even matter since most phone lines no longer charge for long distance**

*Not even available to all businesses in all countries..
( and USA toll free numbers cannot be dialed from outside of the USA..Canadians may be able to dial them ..I won't deal with any USA or any other business that only offers "toll free" it shuts out those of us that do have worldwide VOIP )
**Many countries do still charge very high rates fro long distance /international calls..not all ISPs offer VOIP..and Skype is not available everywhere nor does it work on all platforms and to all destinations..

Skype can still be a very expensive option (when it works ) if both parties do not have Skype..

What your customer saves on a phone call ..they can later spend with you..

All my businesses use PO boxen..

We are no longer a B & M , and do not want "drop ins" where we live..

All our phones ( except business/ customer relations lines and ICANN mandatory contact numbers ) are unlisted..

I haven't found any of those factors to make the slightest difference to my sites, one way or the other.

Sounds silly, but the existence of a favicon.ico. I've found it to be a better indicator of quality than, for example, the existence of a privacy policy page.

For link building where you're trying to convince link partners, the About Us page and Contact Page is important. An About Us page talking about how you're the leading provider of bla, bla, information to consumers is spammy and a web publisher will understand it.

For link building where you're acquiring a mix of article directory style links, WP template links, etc., the About Us page doesn't matter. The fake About Us page is at this time good enough for Google. But a site like that is ranking with unearned links so it doesn't really matter until the algo catches up with the links and/or the fake About Us page.

I'm not sure if Google even uses these pages as a ranking signal, but if they do it's a minor one, probably because of too many false positives if they put too much emphasis on it. Just an opinion.

I think that the nature of Panda, being a machine learning algorithm, means that all of these things are probably ranking factors. Some more than others. Machine learning implies that the factors aren't known beforehand, but rather, are dynamically discovered.

My high level synopsis of how I understood it worked was that human raters judged some sampling of sites and rated them on some scale of trustworthy/good to spammy/bad. The algorithm then crawled the sites and tried to establish some correlations with the raw crawled data (and perhaps some other information, like backlink profiles).

If that's indeed the high level, then anything that correlates strongly to either "good" or "bad" is probably used, even if seems trivial. Strong correlations, I imagine, get more weight than weak ones.

Since it's a machine learning algorithm, I don't think anything is entirely off the table. Things that might go into the "good", "bad" or "neutral" buckets:

- html comments and/or tags injected by "SEO" plugins
- <meta generator=""> tags that indicate an out of date CMS
- old copyright dates
- outbound links to specific, trusted resources
- outbound links to "bad neighborhoods"
- existence, and uniqueness, of common pages
- phone numbers, addresses, people's names, etc
- counts of broken links, unmatched tags
- use of unique images that don't appear on other sites
- javascript or links related to "thin affiate networks"
- other pages that hint at legitimacy (a "jobs" page, for example...or perhaps a "refund policy" page for ecom-looking sites)
- no doubt thousands of other factors

@rish3, very well said. Your understanding of how machine learning would work is aligned with mine.

I'm not sure that links would be on the table for Panda, but as you said they certainly might be. Clearly links are a serious element for Penguin, however.