Google it, fingerprint card number

Transaction Control Number 

https://custhelp.courts.wa.gov/app/answers/detail/a_id/765/~/assignment-of-transaction-control-numbers-%28tcn%29

Process Control Number 

http://www.wsp.wa.gov/wp-content/uploads/2017/12/Process-Control-Number-PCN-Guidelines.pdf

It seems TCN is replacing PCN in the new