Hi Roy,
A lovely Button. I’m afraid I cannot help with the backmark but attached link may be of interest, if you scroll down to Oldham LM you’ll see a description and sketch of your button. It covers other Buttons and Insignia to most of the Lancs LM .
There are records of returns for the OLM up to 1826.
Paul
https://thisreilluminatedschoolofmar...ia-lancashire/