I have just read with interest this question and its answers which covers when it is appropriate to use "du" or "sie".
My question is, is there something that is often said in German which translates roughly as "it's okay, you can address me with 'du'", or do you just generally follow your conversational partner's lead?
Conversely, is there something that is said when someone feels they should be addressed with "Sie" and the person is using "Du"?