I have never seen that symbol before. There is no braille equivalent. I would suggest you use a transcriber-defined symbol indicator (rule 3.26 of UEB). It gives the appearance of some type of grouping indicator...does the surrounding text explain it at all?
Nope. Almost 200 pages into the book and this is the first time it shows up. The surrounding text does not clarify it at all. I think I'll post it to the Foreign Language forum just to see if they know what it is so I can provide a decent explanation when I create the symbol.