The widgetfor displaying specials displays prices with a dollar ($) sign. It doesn't matter what currency is actually set.
The main menu display is fine - it doesn't display a currency symbol at all.
If you want to change the widget displayed currency symbol, open widgets.php in the plugin, and edit the following line:
470 $price = ( !empty($item['menu_item_price']) ) ? ' - $'.
Replace the '$' at the end of the line with the currency symbol of your choice, or just remove it.
For many currency symbols you should use the html encoded version - example: & pound; for GBP.