Cursory examination of the Technology Guide did not reveal it to me, though I may've overlooked it or it might be printed elsewhere such as in the Numeria book.
I believe that is a cosmetic detail, and not covered specifically in the rules. You should be able to assume that anything with charges likely has some sort of display for telling how many charges it contains.
The closest I could find was the battery, which says, in part -
one can tell a functional battery from a destroyed one by the way the circuitry seems to shimmer slightly when reflecting light. The circuitry in a charged battery glows with a soft blue radiance equal to that of a candle.