Unfortunately I have lost or mislaid my old seamanship primers which had the signal codes that gave out storm warnings as visual signals from shore stations. This was still ostensibly in use 45 years ago, before the current era of electronic communications. Obviously it was only useful for coastal navigation in inshore waters within sight of land.
I couldn't find a link to the UK cylinder and cone signals but it seems such signals are still used in Indian and other far eastern ports for storm warnings. here's a link, and as memory serves the symbols and configurations used are similar to the old british ones. Hardly surprising as the Indians used British methods as part of the Empire.
http://www.marinebuzz.com/2010/11/10...ian-sea-ports/
That might give some sort of clue as to what form those early weather signals may have looked like.
Also this one
https://en.wikipedia.org/wiki/Robert_FitzRoy
Admiral Fitzroy who instigated the visual storm warnings and methods of Marine weather forecasting, and who has his name immortalised as that of a Shipping Forecast sea area.
I hope that might shed a bit of light on it.
In the early 20th Century the advent of wireless telegraphy brought about a revolution in both communicating weather forecasts to mariners at sea, but also brought about the first accurate mapping of weather systems by dint of merchant vessels being designated weather reporting ships and required to take a series of meterological observations every 6 hours which would then be coded and transmitted back to the met Office where all the data would be compiled and a synoptic chart produced from which a forecast could be made. The information in these charts was encoded and transmitted back so that it was possible, if laborious, to plot a weather map on board ship.
Andy.