white metal inscriptions on blue john stone ring

by j jack
(Portugal)

I have a blue john stone on a white metal ring from a charity shop where the gem is loose and I will repair it.
There are funny inscriptions on the flat metal part and 2 others on the outside of the ring.
Inside: a 3 centered in a lamp shade box with a small top upper and lower stamp similar to a hammer OR anchor (big part on the under). It does not go through the 'shade'.
In the central flat part are letters in a ovalish circle. Looks like m h e o m o f r on one half, and clearly 250 in the opposite part of the circle. In the centre there is 3 letters HA and M(?).
On the exterior of the band is 2 stamps: SiT and Z11 or 211.

I have used a 10X and 20X jewellers loupe to identify the stamps, but the letters especially are similar to, but?

Blue John gems are strictly from UK (Derbyshire).

And I am in Portugal.

Other metal stamps of gold and silver matching have been none.

J. Jack
Gemmologist