Put a set of X7 thumbshifters without indicators on one of my recumbents a few years ago - I was surprised by the omission but remembered that I had ridden with friction downtube shifters for years and that, as far as I know, brifters don't have indicators.
I can see the front rings, but have to make educated guess as to which rear cog I am on. (On most 'bents, can't look back and see the cassette) On a steep hill, I can tell pretty well when I am down to the lowest cog. Not a problem.