I've never seen any distinctive markings on the British cheekpieces. What Roger says about them being worked on for fitting is certainly true so any markings in the channel could be removed. The cheekpiece you have pictured looks like an Australianpattern for the SMLE HT sniper. If it was sourced in the USA
from Gun Parts Corporation/Numrich, they have their reproductions made to the Australian pattern. If not, maybe it's original. They don't look right on a No.4T or L42. You can source excellent British pattern reproductions from DS Solutions in England
if in need.