Good evening HawkCrossword. That's a new one on me. It's not shown in Chambers Crossword Dictionary along with other such indicators either. But the important thing is to understand that it IS used in that way. Many thanks for the heads up.
Although useful, it's important not to rely too heavily on those lists of indicators. It's part of the development of crosswords that setters find new and innovative ways to code the wordplay. I have started compiling my own lists, which I use in setting. When I complete a crossword, I go through each clue again and add any new ones to it.