Article 41 provides a specific directive for determining the value of supply for postage stamps used for postal services within the State. It explicitly states that the value for tax purposes shall be the monetary amount shown on the face of the stamp. This rule establishes a clear and straightforward valuation method, precluding other forms of assessment like market or cost value for this particular type of supply. The provision ensures a standardised and consistent approach for calculating tax liability on the sale of postage stamps, simplifying compliance for entities involved in providing postal services and for tax authorities.