Sir: The most appealing explanation I have heard for the origin of the dollar sign, $ (letter, 17 December), is that it is a rare example of a pictogram in English. Originally it was written ISI, to depict a river running between its banks, ie a valley or, in German, Tal. The currency thus denoted was the Taler. We can still hear the sound "Taler", in the American pronunciation of "dollar". The written pictogram has been squashed into one character space as $.