HOWTO determine in content page page_load if masterpage fired post

[Guest]

I want to bypass my content page's page_load event when the postback is
caused by a control from my masterpage, doing something like this from my
content page's page_load handler:

Private Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Handles page.Load

If NOT sender.ThisEventWasFiredFromTheMasterPage then
'process normally
end if
(else exit sub, essentially)
end sub

What is the syntax to determine what fired the postback?
TIA,
Berry