Final answer:
Neglect of an older adult client by a primary caregiver can be indicated by the caregiver's failure to meet the client's basic needs and provide necessary care, as well as signs of isolation and lack of support.
Step-by-step explanation:
One possible indicator of neglect in an older adult client whose sibling is the primary caregiver is the caregiver's inability or unwillingness to meet the client's basic needs for food, water, shelter, and personal hygiene. This can be observed through signs such as malnutrition, dehydration, poor personal hygiene, unclean living conditions, untreated medical conditions, or failure to provide necessary medications. Neglect may also be indicated if the caregiver is isolated and lacks social support, leading to the client's physical, emotional, or social needs being unmet.