CAN anyone name this unidentified lawyer whose photograph can be seen in the Legal Department mess? The picture of the twentysomething brunette has been a fixture near the bar for as long as anyone can remember, clad in a horsehair wig and a barrister's ''bib''. Completing the ensemble is a barrister's gown, or rather it isn't, since the garment has been pulled down to reveal her breasts. Legend has it she is a High Court judge's daughter, or a lawyer long since returned to the UK. Women members of the department have fought several campaigns to have her removed, but the most recent assault was repelled with the warning: ''You girls will never get enough signatures.'' Covert action - ripping the picture down - has also failed, since someone kept the negative and the mystery woman was returned to her spot a couple of days later.