Actually, the clerk keys are labled ABDE. The are the last 4 keys on the top row on the right. (They skip the C so it isn't confused with the clear key.
To sign on just press clear and one of the clerk keys: A, B, D or E.
To sign off press 0 (zero) on the numeric keypad and the signed on clerk.
Rick at Direct POS in Boise, ID, January 2010