Not all 35mm SLRs have the film memo holder. Lots don't, in fact. The tried and true way with most any 35mm camera that has a rewind crank is to wind on the crank, taking up slack in the film cassette. When you feel resistance, you know the camera is loaded. But obviously you don't know what film is loaded. What pros often did with cameras that had no memo holders was to use masking tape, taped to the camera back, where they'd write down what was in the camera. I still do this.