They are Rotosound strings.
It's a very good brand of handmade strings made in the UK, I didn't know they were the ones Rog uses until I bought them for my bass player and we noticed that there were some writings explaining that they were the strings used by Waters, John Paul Jones, Adam Clayton, I believe also John Entwistle but I'm not sure, and some others.

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Who was only a stranger at home
Who was ground down in the end
Who was found dead on the phone
Who was dragged down by the stone

No Floyd without Rog

WaterSlut #00000002