Signature In regional language.

One of my clients who is  a professional  is signing his tax returns etc.,in his mother tongue? Can he do so. Is there any restriction that a person can sign only in English especially if he is a professional like CA, Doctor etc., I was told that for incorporating a company the ROC insists only signature in English or notary attested affidavit for Articles of Ass. and MOA.

CA. N. NAGARAJAN.