Visiting friends near Portsmouth last week I took a stroll around Gosport and came across this tide clock. (I'm not sure of the name of the aircraft carrier in the background, but we only have 2 in service they tell me so its either Ark Royal or Illustrious.)
And a nice little mosaic on the pathway nearby. If you look very carefully you'll see the little moon and sun together at the height of the spring tide, I suppose the E in the middle indicates the Earth.
Tide clocks are not that uncommon, but I don't think they can be accurate all the time. They generally work on a 12 hour 25 minute cycle based on a lunar day of twice that. However tides can vary with local geography, wind and estuarial flows. For the Southampton area you can get special solent tide clocks which recognise the double high tides unique to that area.
This Gosport one has a funny little pointer to indicate whether the tide was rising or falling, but whoever designed it failed to make it clear how you are supposed to tell (unless I'm just being dumb).