Well, you sort of can. Give the rear gears (cassette) numbers, 1 being the biggest, and the front (chainset) letters - L and H (or L, M and H) for Low, (Middle) and High. So you can then say 'I was in 7H and the bike was making a noise'. I grant you, though, that it's not very universal. Of course, if I use L and H for the chainset and someone prefers L(large) and S(mall) then that could get very confusing.