Your sister is challenging a property gift deed your father made to you, claiming forgery of your father's signature. While your father is deceased, the property has been mutated to your name and the deed was registered with two witnesses, including your mother. A forensic report may be inconclusive, especially given your father's age at the time of signing. It's crucial to present the attesting witnesses in court to confirm the deed's legality and your father's intentions. While signature variations are possible due to age, a registered gift deed with witnesses is generally strong, but consulting a lawyer is essential for a robust defence.