If Fencer X's mask does not bear the preliminary inspection marks, what action must the Referee enforce?

The correct action is to award a red card and require inspection if Fencer X's mask does not bear the preliminary inspection marks. This reflects the importance of ensuring that all equipment used in fencing meets safety standards. The mask is a critical piece of protective gear, and if it lacks the necessary inspection marks, it indicates that the mask has not been verified for safety, which is essential for the protection of the fencer during the bout.

Awarding a red card is appropriate in this situation as it signifies a serious infraction regarding safety protocols. The requirement for inspection allows for the mask to be examined and either approved for use or deemed unsafe, thus ensuring that the fencer is adequately protected.

In contrast to this option, allowing Fencer X to compete without proper inspection would compromise safety standards. Confiscating the mask might leave the fencer without appropriate gear for competition, which would not be in line with safeguarding their wellbeing. Issuing a yellow card generally signifies a less severe violation and does not address the critical safety issue presented by the lack of inspection marks.