I went on a trip to Canada recently and used my Citi AA MasterCard. One useful feature of Citi online, is that whenever you use the card oversees, you can see the foreign currency amount along side the converted USD in the full charge details, when you hit the little + icon in "account activity" (useful for detecting DCC scams) Anyway, I logged into my Citi online account to check on something else, but noticed something interesting with regard to my foreign charges

Most charges just say 22 Canadian dollars for example but a few like Alamo rental car says 300 CAD and has an "AN" annotation next to it ? Or, a fast-food joint next to YYC airport says 15 CAD , with an annotation of "EQ " next to it in the charge description.
Does anyone know what those annotations on some charges mean? (i asked customer service, but they all say their systems do not show the annotations and nobody has access to my exact Citi online account, except myself)
Any ideas?