by Ken Golliher: Noting that your question is limited to the deposit side, so is the answer. The UCC says an individual's signature is whatever he wants it to be. Your customer should sign the signature card the way he intends to sign a check as, historically, the signature card is used as a source of verification that future items presented against the account are authorized.
by John Burnett: Ken Golliher could decide he wants to adopt an emoji as his signature. That's his privilege, so long as he's not using the signature fraudulently. You'd be correct to accept that signature as his on his account styled "Ken Golliher."