<asp:TemplateField>
                    <ItemTemplate>
                        <asp:HyperLink ID="HyperLink1" runat="server"
                            NavigateUrl='<%# Eval("Post_ID", "~/RCA.aspx?Post_ID={0}") %>'
                            Text="SEND"></asp:HyperLink>
                    </ItemTemplate>

<asp:Button ID="btnRCA" runat="server" onclick="Button1_Click"
                  Text="Assign RCA" Width="147px" />

//When linked to RCA.aspx from Home.aspx, a parameter called ShowButton=1 is included
//in the URL.

<asp:HyperLink ID="HyperLink1" runat="server"
    NavigateUrl='<%# Eval("Post_ID", "~/RCA.aspx?Post_ID={0}&ShowButton=1") %>'
    Text="SEND"></asp:HyperLink>

//By default, since you want the button to NOT appear for all incoming traffic EXCEPT
//that which came from Home.aspx, the button's Visible property is set to false.

<asp:Button ID="btnRCA" runat="server" onclick="Button1_Click"
    Text="Assign RCA" Width="147px" Visible="false" />

protected void Page_Load(object sender, EventArgs e)
{
    //If the querystring has a parameter called ShowButton and it's equal to "1",
    //then set the button to Visible = true.
    //Else, do nothing, keeping the button in it's default, Visible=false state.

    //By putting this in an "IsPostback == false" check, you can guarantee that this will
    //only  happen on first page_load, and won't be triggered again even if you do other
    //actions in the page that cause Postback

    //For example, if you don't use this !IsPostback check, and you end up creating some
    //new function that causes the button to be hidden again, but then you make a
    //selection from a dropdown list that causes postback, you will trigger the call to
    //make the button Visible again, even though that's probably what you don't want at
    //this point, since your other new function set it to Visible = false.

    if (!IsPostback)
    {
        if (Request.QueryString["ShowButton"] == "1")
        {
            RCAbtn.Visible = true;
        }

        if (Request.QueryString["Post_ID"] != null)
        {
            //do whatever you need to with the post ID
        }
    }
}

Response.Redirect("RCA.aspx?Post_ID=1234"); //button will be invisible

Response.Redirect("RCA.aspx?Post_ID=1234&ShowButton=1"); //button will be visible

string currenturl = Request.Url.ToString(); //get the current URL
string urlToSend = currenturl.Substring(0, currenturl.IndexOf("?")); //cut off the QueryString entirely
urlToSend += "?Post_ID=" + Request.QueryString["Post_ID"]; //re-append the Post_ID

protected void Page_Load(object sender, EventArgs e)
  {
        if (Request.QueryString["Post_ID"] != null)
          {
             btnRca.Visible = true;
          }
   }