Generally all manufacturers use a different color disk or mark the anvil to differentiate between different primer types of the same dimensions. Looking at new primers side-by-side while you are still sure which they are should help. If you are not sure about a loose primer that you find simply throw it away instead of guessing, it isn't worth that much!
Now, a bit of hearsay from another member who claims to have known an employee at CCI who had access to their primer specifications. He reported that his source confirmed that all dimensions, including thickness, and the primer pellet weight, were identical for both the CCI Small Rifle and Small Pistol! In other words, aside from packaging they are, or were identical! I realize this is counter-intuitive, and at odds with popular belief, but that is what was reported. Take it for what it is, hearsay, but this would explain why you don't see any difference!
I can tell you this, I have experimentally loaded identical loads in .357 Magnum with a different manufacturers Small Pistol and Small Rifle primers. The result was there was no discernable difference in ballistic performance when the loads were chronographed! There was a measurable difference when their Small Pistol Magnum primer was used!
I wouldn't hesitate to use Small Rifle in handgun loads, at least for revolvers, but I would be hesitant to use Small Pistol primers in rifle loads just on principal.