if you add your blog url to your signuture and you have 70 posts does adding your blog url to 70 posts at the same time not good for google
I don't think so it is going to harm you as not all the posts will be indexed by the Google at the same time. So it should not be counted as spam links.
Who said its not good? Its a way of creating backlinks and driving traffic through forums and other online communities. When you are contributing something into the community, in return, the community gives you traffic and backlinks.
You are right C.Rebecca, I totally appreciate your posting.. this will create backlinks, drive relevant traffic to your blog or site.