I have read many questions asked in SEs I have not joined yet; the sidebar advertises new hot questions and the top questions of many SEs are worth reading.
Whenever I read an really awesome answer (or a question) on such a SE site, I wonder whether I should join the SE just in order to upvote the answer (or the question, respectively). I know my behavior will have only a minor impact on SE sites, but I look for a general policy which is, in some way, good for SE if followed by all persons who are in such situation.
Is there any such policy? Or should I just do not care about voting and do whatever feels right at the moment. (In the past I have both joined the SE site and simply ignored the upvote button.)