? about British Police uniforms

I found this picture on wikipedia of a Bermuda Police Service constable:

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What do the 3 stripes on his cuff indicate? I would logically assume rank but I have never heard of a British or a British style police force using such a system - based on what I know the present style of police rank insignia in the UK has not changed much since the first British police forces were created.

But I have often seen pictures from late 1800s or so where the officers would have like some sort of armband worn on the lower left cuff ... what did that indicate?

It's a duty armband. This was worn to signify that the wearer was on duty, as policemen were required to wear uniform at all times. Latterly, the stripes on these were always vertical, but several UK forces wore horizontal stripes like this in the nineteenth and early-twentieth centuries.

The horizontal stripes were fairly common both in the UK and in the Empire, although vertical won out in the end.
The colours also varied between blue and red.