From the Did You Know Trivia dep’t: …..

For the US and Canadian market Citroën affixed a plate to cover the choke control symbol on the choke control knob in the SM.  Where you see the word ‘CHOKE’ in an SM, if you peel away that plate, you will see the original symbol underneath.  

Presumably this was done for the North American market because the symbol for the choke was somewhat confusing.  It actually looks looks like a ‘headlight-on’ indicator or some means to level the headlights.  After a few missed starts and lousy running engine experiences for those unfamiliar with the control, the idea to place the word ‘CHOKE’ on the knob, probably made a lot of sense.