As per my knowledge as a contract employees employer we can mention Bank account number of the employee at the employee signature place, and also a paid proof your can submit RTGS reference numbers also. This type of process is accepted in Tamilnadu, karnataka, Telangana, Delhi, UP, Haryana.
There is no need to take their signatures.
I wish to point out following for information;
1. When salary is paid through bank transfer in the account of the employees, the signature on the wage register is not required at all.
2. You need to maintain virtual salary register with transfer details.
3. In olden times signature was mandatory as the salary used to be in cash and hence acknowledgement was required as a proof for payment of salary/wages.
4. This a recognized practice by the government authorities.
5. Our Prime Minister has been advocating this hence the digital proof to maintain the payment and its trail is there.