In volume II of Montag's double bass method, I found these signs above the staff which look like they should be bowing signs. My guesses for the arrows are either alternating down-bow and up-bow or whole bow. My guess for the sign that looks like a rotated rest would be "frog".
What do these signs mean? Are these standard signs or are these Montag's invention? (They are not explained in that volume – maybe they are in volume I.)