Yes, they're Ministry of Supply examiners. These usually operated from the outreaches, such as Fazakerley, Maltby and you'll see them on weaponry, usually pistols but on other stuff too, that's passed through the 'in-inspectors' at Woolwich. When stuff has gone through Woolwich, yoiu'll usually see the letter W with a crown over the top. Someone has shown a good enlarged picture of this in the past