It would be easy enough to produce a factory photo showing none for 71. Many bikes were re-fitted with them because of the I didn't see the bike excuse used by cage drivers for many moons. It seems all the young drivers around here are confused by hand signals. All 1973 and on bikes had them the rest is up to you.
Whether or not a Commando had turn signals depended on where it was to be delivered. The 1971 wiring diagram shows signal wiring. I have never seen a '71 in the 'States with turn signals. In fact, many '72 and '73 models didn't have them either. My own '73 Roadster was shipped without them, but a friends '72 Interstate had them from the dealer.
Mine is a 71 too. I'm in Alberta and to pass the provincial inspection recently, (it came from Winnipeg Manitoba) I had to reinstall the turn signals. The turn signals were a requirement here effective Jan 1, 1971. My wiring harness was well molested over the years and included a four pin trailer hitch connector amongst other things. It was easiest to just gut it and start over. If your wiring harness is intact or close to it you may get away with just plugging the signals back into the harness. If it's a mess I'd buy a new harness. They weren't expensive and install easily with a minimum of fuss.
May the Lucas gods smile upon you!