According to this casino description of the game's rules:
Bank Handling in Chemin de Fer
The player sitting on the right side of the croupier, who is based in middle of the table, is first to be the Banker. ... The players take turns in the role of the Banker.
.... There is no need to worry about the rules of Chemin de Fer – they are watched carefully by the croupier.
The above makes no mention of aids at all, only that the croupier will ensure errors in procedure are corrected; so presumably one may possess and refer to memory aids in regards the rules as needed.
Further there is no requirement, either by the Rules or strategic considerations, for the Banker's dealt cards to remain hidden once the Player has announced to Stand or Draw. A Banker may thus freely turn them over after that Player decision is made, either for assistance on the Rules
or to demonstrate compliance with them.
That said however; redrawing the chart above as follows gives a much simpler rule for the Banker to follow:
Except for the combinations 9-3 and 4-5, the Banker must Draw when the Player's third card is:
- equal or greater to twice his initial hand value less 6; and
- less than or equal to 7.