It's not valid if there are no signatures on it. The certificate bears all the above signatures. 

Sir,
If you need any further assistance.You can approach me through Kaanoon or LinkedIn.

the certificate issued by marriage officer  on 6th July 2021  is valid 

The certificate is perfectly valid. It is digitally singed by the Competent Authority/marriage office. Though in the Fifth Schedule under Section 16, there is provision of signature of bride groom, bride, three witnesses and marriage office, no such physical are required on digital certificate.

home office is only concerned with the fact that marriage certificate has been issued by the competent authority ie marriage officer 

you can file affidavit that marriage was registered  under provisions of special marriage act in presence of 3 witnesses 

As stated in the disclaimer, certificate can be verified by visiting the link mentioned in the certificate.

It's displayed on the certificate

- Since, you have registered the marriage under the Special Marriage Act , after appearing before the marriage Registrar with the three witnesses , then that issued documents must having certified signature on a separate page or on the back side of the certificate. 

- However, if the said certificate has been issued online and having digital signature of the Registrar , then physical signature is not required. 

- Further, as this marriage is already registered , then this certificate can be checked at the time of visa from the website for its authenticity. 

The marriage certificate has to be seen to render a proper opinion in this regard.

If you suspect that the Visa may not be entertained in the absence of the signatures of the parties to marriage in the marriage certificate you may better clarify the same with the concerned registrar officer and get the issues rectified.

If there are an y QR scan code appearing in the marriage certificate, any authority can scan the code and get the details of the certificate and may ascertain the validity of the same.

If there is no such facility is available then the authorities may question its integrity and may even ask you to produce an authenticated document in this regard.

The disclaimer note found in the certificate clearly indicates that how the veracity of this document can be verified for its correctness.

You have a certificate issued under special marriage act. It is not issued as per the marriage registration act. So get it issued from your local authority municipality/ corporation/ collectorate. Usually it insisted by persons who are planning to go abroad.

Dear Client,

                    If signatures are illegible clearly, the certificate cannot be accorded with value of a marriage certificate,Hence, such a 2 certificate cannot be used.There may be occasions where a couple will have insufficient time to obtain a marriage certificate after their marriage. For example, they may be travelling abroad on their honeymoon very soon after the marriage ceremony. In these circumstances you may wish to complete and give them Acknowledgement Form at Appendix O. This is a non-statutory form, which confirms the details of the solemnisation of their marriage only. However, they must be warned that it is not a marriage certificate and that as soon as practicably possible, they should obtain a marriage certificate from their local register office.

Once the marriage document has been signed it, the member of the clergy who has solemnized the marriage should arrange for the marriage document to be returned to the local register office to be registered on RON. The member of the clergy who has solemnized the marriage may wish to return the document by post or with the agreement of the couple, ask them or a family member to return it to the local register office for the marriage to be registered. Once this has been done, and not before, the couple or their representatives will be able to obtain a marriage certificate.

Thanks & Regards