If you answer YES to “Do you feel that your financial circumstances might qualify you for an application fee waiver” on Common App, you are presented with a list of qualifying “indicators of economic need” - including ACT/SAT test fee waiver, Federal Free or Reduced Price Lunch program, USDA Food & Nutrition Service Income Eligibility Guidelines, TRIO, Upward Bound, any form of public assistance, federally subsidized public housing, being a ward of the state, and finally a “supporting statement from a school official.”
Whether or not the GC includes hardships in their LOR, the applicant can signal their economic status by simply answering the Common App question. I am certain that AO’s know the income thresholds that lead to FRPL, TRIO, USDA…