What is metro transfer pin?

As an AI language model, I don't have full context about the term "Metro Transfer Pin". However, based on general information about metro transportation systems, a "transfer pin" might refer to a ticket or pass that allows riders to transfer between different metro lines or modes of transportation such as buses or trains. This pin can be inserted into a turnstile or scanned at a gate to allow riders to change from one metro line or mode of transportation to another. Passengers may need to pay an additional fare or use a transfer pin to use a different metro line or transportation mode than their original ticket purchased.