Self signed share certificate

The signature in the capacity of the authorised signatory/secretary is very much valid. 

Since the MC is stated to have been superseeded by new MC accordingly new Secretary has been substituted by a newly elected Secretary, therefore, previous Secretary has "no" authority to issue Share Certificate, hence it is illegal and invalid.

Sorry for the misunderstanding, but the share certificate was issued when the previous committee was in power.

It is valid if the share certificate was signed by Secretary of MC when it was still continuing.

It is strange that one is allowed to sign his/her own legally valid documents to show the right of possession.

It is not strange but a legally valid act 

Understand the concept that an authorised signatory is exercising it's authority by signing the certificate in its official capacity, even though the recepient is the same person.

There's no legal infirmity in this act.