The more I look up the markings on this No. 4 I just acquired, the less I know. So I'm turning to the forum.
First, there's an "FR" on the stock, which I've seen can mean a few different things. The buttplate looks like Zamak rather than brass (e.g. compared to my No. 1).
The left side of the ring just above the trigger has the following:
N
12--- (5-digit number)
AN15-- (AN followed by 4 digits)
Then a little ways below that is two horizontal lines, almost like an equal sign (top line is a little longer, and is even with the top of the letters), and ".T.R"
It's marked as a No. 4 Mk. I, but it has Mk. II sights. There're a couple of the crown stamps, one just above the Nock's form and another on the bolt handle.
The bottom of the stock, just behind the trigger guard (so where the shooting hand would rest) has these:
M
(crown image)
T (rotated 90 degrees)
T
On the bit of the barrel that extends past the forestock, there's what looks like an "X" or crosshatch or something. Then it says ".303 2 22" " ... on the next line it says "18 (high dot) 5 TONS"
The barrel crown has a tiny (3mm or so) section that's threaded.
I can try to do pictures, but I only have a cell phone so it doesn't share details well. I'd appreciate any information y'all may have.