fix for Wordpress displaying 'HK$' symbol
Wordpress seems doesn't show the HK$ sign even with currency set as Hong Kong Dollar. After doing some research, It is found to be a known issue for woocommerce's theme.

Make it work for Hong Kong Dollar
The fix is easy. Just open the Theme File Editor and find functions.php. Append the following code at the end.
/**
* Change a currency symbol
*/
add_filter('woocommerce_currency_symbol', 'change_existing_currency_symbol', 10, 2);
function change_existing_currency_symbol( $currency_symbol, $currency ) {
switch( $currency ) {
case 'HKD': $currency_symbol = 'HK$'; break;
}
return $currency_symbol;
}