Interesting thread drift
Some years ago, in joining the circuit at FACT I had a controller instruct me to position myself "behind ZS-ABC" or words to that effect. I replied that I could not read the rego so he huffily re-phrased to "behind the Cessna on short final". My situational awareness gave me a fairly good idea of which A/C was ZS-ABC but I could not be 100% certain as I had just come on frequency & was also concentrating on other things - was the controller wrong to use the rego for identification purposes?