Users often post homework questions to MSE without tagging them with "(homework)." If I suspect a post is such, I treat it with skepticism. I will either ask if it is indeed homework or not answer it at all.
Other users often post problems from book which they are studying on their own without mentioning their self-study. I treat these as those to which I refer in the previous paragraph. If the user had mentioned this was indeed self-study, I would be more charitable in my response.
While it would not fix the second problem perfectly, I think a "(self-study)" tag might help. What do others think? Is there any reason not to provide such an option?