[DonVoigt]

The crown/x is just another inspection mark, belonging to an inspector who's last name was X.... or perhaps a special inspector that "approved" parts after the Revisions Commission approved its release, JMHO.

I see no reason why it is anything else or an attempt to obscure another mark.

We commonly see C/B on replacement parts which are not numbered, also perhaps a name or a stamp used for specially gauged parts for use as replacements. For example they could have been chosen for their close adherence to tolerance and deemed more likely to be a "universal" fit.

Or they may simply be inspectors names who were assigned to these duties due to seniority or other special consideration. Again JMHO.