This maybe moved if not in correct subject head.
I've used different methods to determine what film I have in my camera. Reason, many times I will have different films in each camera and use based on conditions and what I want to accomplish. With Leica some have the circular piece but that tells speed not type of film such as Pan F Plus or Delta 100 and so on.
To help me remember what film I have in my camera I now use Post it Notes page markers. I write the type of film in the camera, using a sharpie pen then either putting it on the base plate or the bottom of the case the camera is in. They fit with no overlap.
Thought I would mention it here to help.
Here is a plsce to buy them: