How to check if Page is from Server.Transfer but ignore Clicks?

[CyB3r.K!nG]

I want to check if a Page is reached by a \[code\]Server.Transfer\[/code\]. So I checked if \[code\]PreviousPage\[/code\] is null. But when a user clicks on an Asp.net button - it is. So how can I ignore those and check for how the user originally got to this Page?