You can assign a single event to multiple button clicks -
topButton.Click += SignInButtonClick;
bottomButton.Click += SignInButtonClick;
void SignInButtonClick(object sender, EventArgs e)
{
//your code here
}
I presume in your case the same logic will run for both buttons, you could find out which button was clicked using sender argument that is passed into the function.
As an example, let's say I have an aspx page and I add a button to it called 'Button1' I can then add a click event via Visual Studio and it will create a methiod to handle the click event for me called Button1_Click. The method will be automatically linked to the button as the AutoEventWireup up property in c# is set to true by default.
Now, if I add a second button and call it 'Button2' but I want that button to fire the same event handler as the one used for Button1, I could add this code to the pages 'Page_Load' event handler
Button2.Click += Button1_Click;
Both buttons would then cause the 'Button1_Click' method to run when clicked.