The aluminum model has a red circular sticker near the clamp area that reads heat treated, although perhaps that is missing from yours. The aluminum model is rather light and has a brighter finish than the chromoly which has more of a soft, satin finish.
I concur with Joe B, the aluminum bar has hash marks at the clamping area, although they seem to disappear quickly if you change out the bars a few times.
All of the Nitto/Rivendell albatross bars I have owned have a model number and a width designation at the end or ends of the bar.
- Frank