At Swanwick, the area side anyway, anything squawking Ident gets a flashing circle around the radar return.
It's not a mandatory readback so I'm not fussed if pilots don't say anything back to me, although most do.
I've only ever heard the "flash" term being used by US Military pilots so I guess it's one of their things, although to be fair I've never had to change the squawk on civil US carriers so it could just be an American thing