If there is a question and it is specifically answered from something you posted somewhere else, I do not consider posting a link to it spam.
If your post history is nothing but that though, I will consider it spam. Yes, you are technically posting relevant answers, however, continually pointing at posts you make somewhere else...the likelihood of you happening to coincidentally specifically answering those questions somewhere else becomes a lot smaller than you purposefully answering them on your own site and linking the answer here to promote your own site.
So yeah, it is heavily circumstantial, a judgment call, based on posting behavior.