How to display a product is ON SALE....

Hi,

I want to display that a particular product(s) is on sale. i.e to provide a chkbox IsOnSale in the ProductVariantDetails.aspx page similar to the Is Gift card chkbox.
When the Administrator selects the IsOnSale chkbox for a product ..... an image or an label with bold fonts should be displayed in the public store for the customers indicating that the product is on sale.

So, I have included a chkbox IsOnSale into the ProductVariantInfo.ascx , added a new colomn into the Nop_ProductVariant table and also included the
        
         public bool IsOnSale { get; set; }

in ProductVariant.cs file....... but I am not able to figure out from where the ToolTip and Text values are assigned in the ProductVariantInfo.ascx

Eg:
<td class="adminTitle">
            <nopCommerce:ToolTipLabel runat="server" ID="lblIsOnSale" Text="<%$NopResources:Admin.ProductVariantInfo.IsOnSale %>"
                ToolTip="<% $NopResources:Admin.ProductVariantInfo.IsOnSale.Tooltip %>" ToolTipImage="~/Administration/Common/ico-help.gif" />
</td>

from which file is the database values retrived and Inserted???
I also want to know if a chkbox is added into the ProductVariantInfo.ascx, what other pages should be modified .....

Thanks,

Deeps