No Horses or Ponies?

We went for a late walk; what with one thing and another.

We took one of our regular routes around Ardington.

I have always been intrigued by this sign on a mysterious little walkway onto the Ardington House Estate.  Why mention horses and ponies?

I imagine that some years ago it just said 'No Horses' and there was an incident when somebody was caught with a pony; and argued that it wasn't, yet, a horse.  Who knows?