try this may be it will help you.
remember it is only a concept to Show tooltip(or title) message on every dropdown list items,
modify it as your requirement.
aspx code
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem>1</asp:ListItem>
<asp:ListItem>2</asp:ListItem>
<asp:ListItem>3</asp:ListItem>
<asp:ListItem>4</asp:ListItem>
<asp:ListItem>5</asp:ListItem>
</asp:DropDownList>
cs code
protected void Page_Load(object sender, EventArgs e)
{
string[] ar = new string[5];
ar[0] = "One"; ar[1] = "Two"; ar[2] = "Three"; ar[3] = "Four"; ar[4] = "Five";
for (int i = 0; i < DropDownList1.Items.Count - 1; i++)
{
DropDownList1.Items[i].Attributes.Add("title", ar[i]);
}
}