What counts as a Social Signal these days anyway in the eyes of Google?

What counts as a Social Signal these days anyway in the eyes of Google?

Hello all. As we all know by now, with some certainty, social signals count! When it comes to good rankings. It's long well considered that Google does use your social signal count when determining your ranking in the SERPs.

But what actually counts as a social signal that counts? Is it just things that happen on social media sites? You know like likes, shares, reshares, comments etc. But what else is there? And what are they for each social media site?

I've tried to think about what a social signal could be from each top social media site. Here is a list of some social media site and what might count as a social signal. A social signal is basically any form of social activity of some kind.

Facebook
Shares: when someone share something on Facebook (your website).
Reshares: when someone reshares that share on Facebook again.
Likes: when someone likes something that was posted on Facebook.
Comments: when someone comments on something shared/posted on Facebook.
Fans: anytime someone likes your page and becomes a fan.

Twitter
Tweets: anytime your site is tweeted about and appears on Twitter.
Retweets: anytime said tweet is retweeted on Twitter.
Likes: anytime someone likes or favorites said tweet or tweets.
Comments: anytime someone leaves a comment on a tweet(s).
Followers: the amount of followers that you have.

Pinterest:
Pins: anytime a pin is pinned to Pinterest with your website link.
Repins: anytime a pin is repinned somewhere on Pinterest.
Likes: anytime someone likes a pin.
Followers: the amount of followers that you have.

Instagram
Posts: links can't be used in Instagram posts (although people still do). But it would likely be;
Followers: how many followers you have.
Likes: how many likes all your posts have (collectively).

Snapchat
I'm not sure how Google can see this. Does anyone know how or in what way Google can use Snapchat to as a way of knowing how to rank a site?

LinkedIn
Posts: anytime your website is posted on LinkedIn in some ones post.
Reposts: anytime your post is reposted to someone else's profile.

Tumblr
Posts: the amount of posts you have on Tumblr (how many times your URL is shared)
Reposts: how many times the posts are reposted (reblogged) on Tumblr.
Likes: how many times your posts or posts with your URL are liked.
Followers: the amount of followersthat you have on Tumblr.

YouTube
Videos: how many times your link appears in how many videos.
Likes: how many times that video or videos have been liked.
Subscribers: how many subscribers are subscribed to your channel.

Google+
Posts: how many posts your website URL appears in.
+1: how many times those posts are +1'd (liked) by people.
Circles: how many people you have following you in your circles.

Those are just some of the ways that those sites can be used and some or all ways in which they might be used by Google or signals to Google as social activity.

What other social media sites are there that Google might use as a signal to know how to rank a site (based on the guessumption that Google uses social signals as a ranking qualifier) and what social activities would be considered a social signal for each?

By the way, if you've ever wondered what actually counts as a social media site, this social media prism 2016 is a great way of finding out and a good way of finding high authority social media sites you can get on to actually get social signals from those sites!