Change format of product attribute
In uc_attribute.module file comment out from line number 1360 (starts at if ($adjustment != 0) {) to 1363 and add the bellow code 

if ($adjustment != 0) {
    //$display_price = $adjustment &gt; 0 ? '+' : '-';

    //this variable is used to flag your custom discount on minus values 
    $set_discount = false;

    if($adjustment &gt; 0){
        $display_price = '+';
    }else{
        $display_price = '(';
        $set_discount = true;
    }
    if($set_discount){
        $display_price .= uc_currency_format(abs($adjustment)). ' off)';
    }else{
        $display_price .= uc_currency_format(abs($adjustment));
    }
}