A tamper indicating preassembly or kit of parts is provided for protection of a container closure plug receivable in a container opening having a groove or recess formed thereabout. A support ring comprises a radially inwardly directed lip engageable in the groove or recess. A masking membrane may be sealed at its periphery to the support ring. The support ring may further comprise a frangibly attached, inwardly extending, flange or projection. When the plug is received in the container opening and the support ring lip is received in the container opening groove or recess, the masking membrane covers up an upper end of the plug and/or the inwardly extending flange or projection overlaps the upper end of the plug. A protective outer cover may also be provided.