Is it legal for a person having two names to sign documents with different names

It is in vogue that there are two names for a single person as one to call in house and one according to certificates. In some cases of Tamil Brahmins, there is another 'sarma' name christened during their upanayana. The name which is in certificates should be hold in all official documents, school certificates etc., and should never mingled with home name or sarma name. Similarly there are two date of birth to some persons as a date given during the school admission hold good in all certificates but the original date of birth hold good for other horoscope purposes. In such cases the person holding two date of birth should declare outside with the official certificate date only. Nowadays people are very alert and somewhat knowledgeable as they hold only one date of birth for their children and they got birth certificate at the time of birth itself.
If any hold two or three names in different documents they should synchronize them with one as per school certificate by approaching respective authorities with copies of school certificate.

Name of a person is his identification by which he is known. It is a unique thing associated with him. His credentials like Aadhar card or PAN card or educational certificates will be marked with that identity only. When he produces these documents anywhere then his identity is confirmed with those details and any mismatch would raise suspicion. It is very clear and obvious that whenever a person is mentioning his identity he has to mention it correctly and honestly. Using another identity or assuming a fake identity are termed as cheating and misleading others and is punishable under the law. Fake signatures made under any identity are considered as forgery and that is also punishable under the law.
Such acts of cheating are covered under Section 416: Cheating by Personation under Indian Penal Code. There is one year rigorous imprisonment or fine or both for such unlawful activities.

Generally, any person will have only one name and that is the name recorded on his identity cards. Aadhar, PAN, bank account and the educational certificate. All these should have the same name. The name can be a combination of different names. For example, my name is a combination of Venkata Srinivasa and Rao. So the name that is on the identity card is only considered the name of that person.
As far as a signature is concerned, the signature of the person should be the same in all the documents. It should not vary. The same person may sign in some documents in his native language and some documents in English. There will not be any problem as long as the candidate who signed is owing that signature. The problem comes only when the person signs in a different way and afterwards he claims that the signature is not his signature. If a candidate intentionally signs in a different way and tries to deceive other people, it is illegal and liable to be punished. If anybody is cheating another person by signing differently, they will be punishable as per section 416. You have to contact a lawyer and you have to sue him. A qualified lawyer's guidance is required to fight out such cases.

Though a person can have two different names such as Sonu, Ramu and so on but these names are their house names and even in the society they are recognised by such names only. However they do have the different names in the schools with the different date of birth. Since this name has been entered in the school register, he would pass out class ten, class twelve and so on with this official name only. His bank accounts, Aadhar Card, Driving License, PAN Card etc do reflect the same name. Hence there is no offence in using this official name despite the fact, he is recognised with a different nick name.
Problem would arise in the event of signing the documents of a person whose name is resembling with his nick name. Under such a situation, if he is caught doing a forgery signature in others documents, he would be punished as per section 416.
Hence a person should understand the legal complications while putting initials in others documents though nick name of the person is resembling with the person for whom forged signature has been made.