My wife and I were talking about the engine coolant temperature symbol on our car dashboard yesterday.
I said I expect there’s a Unicode code point for this symbol. Now I don’t think there is. But there is an ISO Standard name for the symbol. It’s part of ISO 7000: Graphical symbols for use on equipment—Registered symbols, reference number 0246.
A while back I quoted Randall Munroe saying “I am endlessly delighted by the hopeless task that the Unicode Consortium has created for themselves. … These are really hard problems and I do not envy them.” Although the Unicode standard includes an enormous number of symbols, it cannot contain everything.
In my experience the engine coolant temperature symbol is far more common than some of the obscure symbols that have made it into the Unicode standard. One could argue that Unicode should give priority to symbols used in written communication and that symbols like the one above would be low priority. And yet the standard includes many symbols that no one is likely to use in writing. The Unicode Consortium truly does have a hopeless task.