Starting on February 29th, when people use multiuse facilities, including restaurants, cafes, etc., they can write their personal safety number instead of their mobile phone number on the visitor log. It has been made compulsory for cafes and restaurants to log all visitors manually or via QR code due to COVID-19.
The Personal Information Protection Commission and the Korea Disease Control and Prevention Agency introduced the personal safety number to prevent the leak of personal information, including mobile phone numbers, which are recorded in such registers.
A personal safety number is a total of six unique characters comprising four numbers and two letters in Korean. It will appear when people go to the quick response (QR) check-in screen of Naver, Kakao or PASS, which currently issue QR codes. Once you get a number you can use it until the end of the COVID-19 pandemic.
https://www.pipc.go.kr/np/cop/bbs/selectBoardArticle.do?bbsId=BS074&mCode=C020010000&nttId=7171#LINK (Korean)