Sure Google recognize the signature links and depends that it should be put on the do-follow forum, In my opinion forum signature links have good value, ya I am agree that has no a huge value as they were before but still now have a great worth.
Again, it is all about relevance. So the more on-topic the links are to the page displayed, the higher the value of the link.
It depends if the forum is do-follow if it is, then the links are given value for SEO related purposes if it is no-follow then it isn't given any prominence
Yes, Signatures in the posts are really useful. search engines crawled that links and given preference if these links are in do Follow.
Sure, Google recognize signature links buy only do-follow. This is the reason why forum posting is a way of link building as well as other activity.