Hallson Gardens

Hi gardeners
Can somebody please tell me what a small cobble sized smooth rock tied up like a small parcel means in a japanese garden.
I have seen this twice while looking at pictures in a book and on the net usually placed on a path

I belive it is supposed to be a rock brought back from far away, and an indication to the guest to go no farther on that path.

Hi,
If the rock tied up is on a path it means, this pathway is forbidden.
George.

Thanks to John and George for explaining the meaning
Regards Brian