You have to remember that the TSA actively looks for ANYONE to nail, whether in or out of their scope. They don't care if you have a warrant for a speeding ticket or you're OBL himself, they will not hesitate to use you as a trophy for their "usefulness."
Holding some copy of a check isn't going to mean squat to a TSAer or even an LEO. The fact of the matter is, you could have just copied it without sending it. If I were a cop, I wouldn't care about some copy
If you are as worried as you seem to be about this (otherwise, why would you post), you shouldn't be posing this question here, but rather you should be doing the right thing.