Our deeds make specific reference to the 'T' markings and state that these markings identify the ownership/responsibility in respect of boundary fences.
In real life I suppose you speak to your neighbours. When I moved into my current home my neighbour told me the fence between us was his fence. I have no neighbour at the other side or the back so I was happy for him to claim that one as his! I would just say don't repair/replace a fence you didn't pay for/have put up without checking with the neighbour. If anyone is in the postion of thinking a neighbour should replace/repair a fence I would imagine they have little recourse for actually getting them to do so.
From personal experience, and out of courtesy, whenever i have done boundary walls and fences the "face side" has gone to the neighbours. Never been an issue personally, unless they were disputing measurements. Responsibility never bern an issue either. Just got in with it , having suggesting to the neighbour my intentions prior