It's in the instructions for the CTR, listed under Item 14, bottom right corner, page 3 of the form.
Unfortunately, to save copying or printing costs, most banks don't include pages 3 and 4 of the form when they reproduce it for use. Those pages have the instructions for the use of the form.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8