This info is passed through the code like:

if(!empty($CNF['FIELD_PRICE']) && !empty($aContentInfo[$CNF['FIELD_PRICE']]))

     $sPrice = _t_format_currency((float)$aContentInfo[$CNF['FIELD_PRICE']]);

The function _t_format_currency takes the default values of in the payment settings. So you need to edit the code like above to get rid from this signs in your Ads. But in this case, you will have loose the advantages of the automatic upgrades.