[Yeti]

If the vehicle in your sig is correct you don't have one since it was not even an option in '10 in NA. But to answer you question you would have two symbols that look similar. one would be in the 3 o'clock position and the other the 6 o'clock position on the diff knob select surround. The first is the center and the second would be rear. No symbol at the 6 o'clock position means no rear diff lock. The center console with rear diff lock would look like this:

 

[Yeti]

It is not going to be an easy install after the fact and probably cost prohibitive. I can't personally see it as a must have option other then to say you have it. I have rarely used the center lock on mine and when I have been on trail rides where some of the leaders said to lock rear diffs if you have them I couldn't since i didn't and got through the same area they did with out it. It would have to be an extreme situation for you to ever need it imo. I personally would not give it any thought. The screen you saw is just the default one on all of them whether you have a rear locker or not. If I remember, been awhile since I saw that screen, I believe there is even a front position which was never available as far as I know.