Help with Burberrys overcoat

This is my first post on Style Forum – I’ve read and referred to the site for a while now but decided to take the plunge and become a registered user.

So my first post is a question for the learned members – I’ve just recently bought a second hand Burberrys trench coat which I’m very happy with but while inspecting it I came across this tab – for the life of me I cannot fathom what it’s for. It’s located low down on the left inside hem of the coat. Both ends are stitched to the coat though the stitches on the pointed end could be temporary. What’s more perplexing is that there is no corresponding button on the other side of the coat or anywhere near the tab.

Does anyone have any idea what this might be for?

Thanks and best,

David