Your guess...

I prefer to drive to my mum's (t0 sort the loft out) via the Udimore road rather than struggle through Hastings, plus the views are better!
There is a hamlet along the road that is only signed on the way home - massive signs on each side of the road, welcoming careful drivers etc - nothing that I remember seeing going the other way.
Being an infantile 50 something-ish I have always been pathetically amused by the sign.
Is it a disease (I tend to assume fungal)?
Is it a pastime, solitary or otherwise? (Google's 19th entry is "DIY in Cock Marling"...)
Or perhaps it is just a folksy East Sussex place name for a hamlet with pretty little cottages.