If you write a check to yourself from one bank and deposit it in another bank do you have to endorse it? I, Matt Hames, write a check to Matt Hames, sign it with Matt Hames, and then deposit it into Matt Hames' account using a Deposit Slip that I, Matt Hames, fills out.
Turns out, you do have to endorse it. Thus, I'm telling the bank that yes, I endorse the check to me, made out by me, in front of you.
Banks are stupid.