First of all, there is no international global currency symbol table, that anyone on the planet could read and understand.
In each region/country the currency symbols will differ, that`s why you must determine them based on who is reading, using the browser / user locale.
The correct way is as you guessed, using NumberFormatter::CURRENCY_SYMBOL, but you first have to set the appropriate locale like en-US@currency=JPY:
$locale="en-US"; //browser or user locale
$currency='JPY';
$fmt = new NumberFormatter( $locale."@currency=$currency", NumberFormatter::CURRENCY );
$symbol = $fmt->getSymbol(NumberFormatter::CURRENCY_SYMBOL);
header("Content-Type: text/html; charset=UTF-8;");
echo $symbol;
This way the symbol will be understandable by the user.
For example, $symbol will be:
- Canadian dollar (CAD) : CA$ in USA, CAD in Romania , $CA in Iran
- Iran Rial (IRR): IRR in USA, while in Iran will be ﷼