If your scope is not a model with BDC (Bullet Drop Compensation) I would say your assumption they are reference marks to gauge distance is correct.
I have a Cabela's scope that has similar markings. It is just used to bracket targets of known sizes at a known distance to help you with hold over. Once you learn how many inches the marks represent it becomes a faster mental calculation if you need, for example, 4" of hold over at 200yds.