FCC labeling for exempted product (test equipment)
I believe that exemption only applies to devices that are classified as "unintentional radiators." You also should be aware that:


  The operator of the exempted device shall be required to stop
  operating the device upon a finding by the Commission or its
  representative that the device is causing harmful interference.
  Operation shall not resume until the condition causing the harmful
  interference has been corrected. Although not mandatory, it is
  strongly recommended that the manufacturer of an exempted device
  endeavor to have the device meet the specific technical standards in
  this part.


In order to reassure the buyer that they are not at risk of being ordered to stop using the equipment, it would be prudent to test and mark the device or provide a statement about compliance.

Reference