They are both correct. The only difference is this:
In "Si tú hubieras firmado ese contrato..." we are using the personal pronoun tú that you can easily drop if you want to and would still be ok -> "Si hubieras firmado ese contrato..."
In "Si te hubieras llevado el paraguas..." we are omitting the personal pronoun tú that you could add if you want to. The "te" here comes from reflexive verb "llevarse" that we can use in this reflexive way to emphasise who is doing the action. It is something like saying "If you had taken the umbrella "with you"...
So the function of tú and te are different.
I hope this clarifies your doubt.
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