Just clicked on Ray's link to the pic of BB's grave and a thought struck me....
Unless Balfour's body was carried away and then returned to the battlefield after 1690 (when all troubles in Scotland were over), how could he have been buried on the field when the army he was part of was routing and suffered up to 1,000 casualties? Nobody would have stopped to dig a grave in a rout! How would such a spot be marked with a huge stone such as the one in the picture? surely not at the time.. " 'scuse us McSporran, whilst we dig a pit for our brigadier's hacked up corpse, carry on chopping around us we'll be finished soon then you can deal with us!"
I am a fairly well developed sceptic so I will posit this as the a potential solution with a view to suspending disbelief:
Someone remembered where he was killed(a survivor). After all the trouble had died down a stone was placed at/near the spot. Possibly the body is buried there, possibly not. A re-interrment?
Otherwise.... I would have some doubts. I didn't visit this precise spot on recent trips so maybe the sign enlightens the visitor...
Anyone know?