we could even do the following: if someone captures a noble and brings him to his settlement, it is customary to create a permanent trade of food of some low number before being set free, like 2,3 or 5 as a sort of special tribute for sparing him and general noble courtesy. Now the point is that you will be motivated to get a noble yourself and cancel that trade without disrespect so it cancels out or just raid for nobles to rank up the 'tribute', we can name the trade deal too. You can still do the signpost thing, but it would be much better if Tom added a 'rumors' field in character sheets then we could write all sorts of fun stuff, including this, in there. In any case, this way the whole noble capture incentive thing ties into the actual gameplay, your settlement grows slightly bigger, that could even be explained as a result of the added respect gained by actions of capture.