Environment Variable for --data-checksum during initdb

I'm trying to remember what environment variable can be set --data-checksum before running postgresql-setup initdb. I know I've seen it but it escapes my recall at the moment. 

The PostgreSQL documentation has a nice page of environment variables for when PostgreSQL is running, but I'm not finding the variable to set during the initdb phase. 

Any help to jog my memory greatly appreciated.

--Ray