The sightings boards should stay:
1. As moggiedog says - some of the "big cat spotters" to tend to rush off to where the sightings boards says people have seen lion, leopard, cheetah, wild dog etc. leaving the other roads quieter and less travelled.
2. Probably 90% or more of people are serious about it and do put the markers where they believed they had the sightings. Some people may have some trouble translating "real distances" to "map distances" which is why the markers end up in "no-mans land", but one can still get a good idea of which road to travel to find that lion pride that was probably no more than 50 m from the road
3. It's just nice to see what other people have seen during the day.
Regarding your suggestion about the old way of waving people down and telling about sightings:
NO - definitely NO. Reason - I've never managed to find that "9 lions" or "male leopard" "right next to the road, 2 km from here" that "you can't miss" that I've been told about in this way. Two years ago I've made a vow never, ever to try and find a sighting that I've been told about in this way again - the frustration levels are just too high
and it screws up ones planned route for the day in any case.
Also, part of the reason why I go the northern parts of the Kruger year after year is because I want to get away from people. I don't want to be waved down to have a chat. I have my friend / sister / mother / whoever with me that I can chat to if I wish, and the other 50 weeks of the year I spent more than enough time talking to other people - don't have to do it in the KNP as well. Maybe anti-social but that just the way I feel. I think it living in a busy city that has done this to me. This is also the reason that I don't do the yellow ribbon thing - if I could be sure that I won't be waved down for a chat, I'd have proudly displayed the yellow ribbon on my car, but frankly I just want peace and quiet when I'm in the KNP.