It indeed does look to have not not broken the phosphate but as it is a very fine marking is it possible it could have 'dragged' the phosphate down when punched ?
......yes now you mention it,it does look very symetrical between the T and star.

I have not seen the mark before on the limited number of 0T and CH 7.92 Brens I have viewed,is this a mark found on Chinese contract Inglis Hi powers ?

Many thanks for the responses so far.
ATB Kevin