Is it wrong to display elsewhere on the same lines as the name of the institution (trust /society ) and the post of the head of the institution in the private vehicles of legitimate registrars? Is there such thing in the Motor Vehicles Act?

Any altration in the motor vehicle shall be subject to the approval of RTO. ;

No owner of a motor vehicle shall so alter the vehicle that the particulars contained in the certificate of registration are no longer accurate

Till the perticulars in the Certificate of registration are exactly as that of the M V ,there is no altration. 

The Body of MV must be painted in the same color as on Reg.Certificate though adding any signs or names or phrases on the body of MV may be in derogation of rules of the conecrned state or area if so notified by the Rerg. Tran. Office, otherwise not.

You can use the Symbol.