Interesting, brakedwell. Could well be. They were there in the 1968 aerial photo, and I post below a photo I took in 2006 of the last surviving one, just before the threshold of the NW facing runway (it must have been about 29). They were already tearing up the remains of the site for housing and by 2009 it had gone. The markers were white-washed rocks. They were quite big (about 15m long), as you can see from the photo, and were even visible on Google Earth.
Laurence