You need to use common sense and good judgment when determining if something is spam. Posts like "+1" and similar posts are clearly spam unless there is other information in your post, such as why you like the post and/or why you agree.

If something you post has nothing to do with the conversation in the thread, nor anything to do with the original topic then your post is spam.

If you follow these two guidelines then you can avoid having the majority of possibilities of spam posts removed.