I also dislike "ID" vs "id" (as short for "identity"), but there is some case for it. The below are from Webster's Third New International Dictionary Unabridge

I also dislike "ID" vs "id" (as short for "identity"), but there is some case for it. The below are from Webster's Third New International Dictionary Unabridged. First, the case for "id": id abbreviation 1 [Latin idem] the same Now for "ID" ID noun, plural ID's or IDs [REVISED] [identification] 1 a : documentation bearing identifying information