Hi,
As Jerome said, you could change the line:
$this->values[] = JHTML::_('select.option', (int)$currency->currency_id, $currency->currency_symbol.' '.$currency->currency_code);
in the file administrator/components/com_hikashop/types/currency.php and remove .' '.$currency->currency_code to not have the code, only the symbol.
However, it would be better to do an override of the module via the template manager, and copy/paste the code of the type and modify it there.
That way, you wouldn't loose your changes after each update of HikaShop.