If you happen to be in London's West End on Charing Cross Road by the Garrick Theatre have a look across the road and you'll notice a piece of pavement/tarmac that isn't used. In fact it is surround by bollards.
Underneath this piece of space/pavement is an underground toilet/disused no doubt closed by the council. Now if you walk into this area and take a peak at the lower part of the Westminster bog standard bollard (sorry couldn't resist that toilet pun) you'll see the words "STRICTLY NO DIGGING" with the telephone number underneath.
The signs only appear on the side of the bollard facing inwards to this space/pavement area and if you did happen to dig here you'll end up in an old public loo/bathroom area.
Bollards of London...