I found a document Army Form B 59 - Army Reserve (Special Reservists). Grandad Johnny signed his name on the document, however I found the wording of his 'Oath to be taken by recruit on Astestation' most interesting."I John Anderson swear by Almighty God that I will be faithful and bear true allegiance to His Majesty King George Fifth, His Heirs and Successors and that I will as in duty bound, honesty and faithfully defend His Majesty, His Heirs and Successors in Person, Crown and Dignity, against all enemies and will observe and obey all orders of His Majesty, His Heirs and Successors and of the Generals and Officers not over me. So help me God'.
Non-ceremonial flag of the British Army