To authenticate aadhaar signatures, one can use the physical signatures of the clients. If you hold any previously signed documents of the same person, then you can compare the digital signature with those samples. However, Aadhaar Signature Verification is already being done by the service providers as they are authenticated by using biometrics and OTP on the registered mobile numbers. It is always advisable to use the Esign services of a trusted company such as Meon in order to protect your data and documents.