I am sorry to say that unless you know the owner and unless you are the rightful beneficiary, you cannot encash the bonds.
If you don't own the bonds, you need to prove that you have a right to cash them. For example, if the bond owner died and you are the beneficiary, you'll need to identify yourself and bring a certified copy of the owner's death certificate to the bank.
Thus, you may not be able to encash the same without this.
I hope this would help...