582372 150 are the numbers I see. This has been used with teeth marks, small nick out the of wood as seen in the 3rd pic. Small circle or O on the top of the stem. IT APPEARS TO HAVE BEEN BROKEN OFF AND IS NOT INSIDE THE PIPE.
Very cool find. I have the original Underboar catalogue, but have never actually seen one 'in the wild'. Catalogue is on the Charatan pipedia page in it's entirety.
And your pipe shape in the catalogue: