A friend of mine deals with this by occasionally including "if you read this, please leave a comment, even if it's just a period, so I'll know people saw it" at the end of their posts. That seems undemanding, in part because they're explicitly saying "tell me you read this" rather than "indicate that you agree/support me," but in general I wouldn't want it on my own posts. I think that's best handled individually by the poster (who can certainly copy and paste that text if they use it repeatedly) rather than built into the code.