I frequently work with financial documents that use bond ratings, which are: AAA, AA, A, BBB, BB, CCC, CC, C, D, Aa, A, Baa, Ba, B, Caa, Ca, C. They are frequently used in running and lengthy text, along with headers and tables. Sometimes a few of them have minus signs. So, my natural inclination is to use small caps, but I’m worried about the single letters seeming odd or out of place. On the flip side, it seems confusing/inconsistent to SC on only some.

Does anyone know of a hard and fast rule for this? I referred to Bringhurst and it seems to boil down to my judgement or convention as long as I’m consistent. I’m on the fence about sacrificing the overall texture for consistency by using with the full capped versions. The trickiest part in making that judgement is that ratings aren’t acronyms, they are what they are, so I’m inclined to use the full capped versions. Thoughts? Opinons? Just go with whatever?

The font I’m using is Whitman, but this is a general typographic question.