I found the phrase Volta Brackets on a web site listing orchestral symbols incuding those used by the old masters. No other site I found applied a nomenclature it just seemed better than saying, 'you know the sort of thing: those lines with a number which means first time through etc".
Of the two procedures that volovicg helpfully shows, I found using the signature editor the easiest. As you can set the start and finish points by bar,beat,division,click etc. I'd have thought that was the way to insert them off the downbeat (?).