For the 1950 Census, certain lines on each sheet were designated as sample lines, and the individuals on those lines were asked extra questions. The person on the last sample line on each sheet was asked even more questions (part of the 'super-sample').
Some people did not want to give the answers to the financial questions to the census enumerator. The Census Bureau anticipated this, and gave out a form which the person could send directly back to the Census Bureau. The enumerator's note at the top of the sheet was intended to alert the office so that the information from the Confidential Form could be copied onto the P-1 form.
See 1950 Census: Form P1, Population and Housing Schedule Questions 29 to 33 for All Persons on “Sample” Lines Who Were 14 Years of Age and Over by Claire Kluskens on the US National Archives' site History Hub for an overview of the entire process.
If the respondent still objected, the enumerator was to hand the person a “Form P6, Confidential Report on Income, 1949,” that the respondent could fill out, seal, and mail directly to the Census Bureau in Washington, DC. No signature or postage were required.
The link to the entire series on History Hub is: 1950 Census Blog Series.
For more information on the 1950 Census, see the Genealogy Series 2022 playlist on YouTube from the US National Archives Know Your Records Program. Handouts and presentation slides are available from National Archives Genealogy Series: 1950 Census at the US National Archives' website.
The presentation from May 18 at 1 p.m. ET History of Census Records and the National Archives, by Dr. Sharon Tosi Lacey, discusses how sampling began with the 1940 Census, was increased for the 1950 Census.