Hi there,
In Michael S. Welch's "Great Western Branch Lines 2 - Rural Wales", there is a photo of No. 7442 with chalk markings on its smokebox door which may be the one you are thinking of. The writing says "New Valves", and there seem to be some initials - RC and WJ, it looks like. There is also a series of numbers, which could be 11462 or 1/462 (I assume this is a date, but of course it could be something else.