The coated glass is marked, though sometimes cryptically. ("East side.")
The etched reflection control should be used with the fuzzy/etched side facing away from the art. If you put it toward the art, it'll look pretty much like clear, but more expensive.
You'll be able to tell when you put the glass on the art. If the reflections are crisp, it's backwards. If the reflections or soft and fuzzy ("controlled") it's right.
It used to be etched on both sides. The first time I used the single-sided RC glass, I called the distributor to complain that I had a box of clear that was labeled RC.
They told me to flip the glass over.