Rainich=Rabinowitsch (of trick fame : cf. Nullstellensatz).
Here is an anecdote related by Bruce P.PalkaP. Palka, Editor of American Mathematical Monthly in Vol.111 (2004) of that journal (page460).
Rainich was giving a lecture in which he made use of a clever trick which he had discovered. Someone in the audience indignantly interrupted him pointing out that this was the famous Rabinowitsch trick and berating Rainich for claiming to have discovered it. Without a word Rainich turned to the blackboard, picked up the chalk, and wrote
He hen then put down the chalk, picked up an eraser and began erasing letters. When he was done what remained was
RA IN I CH
He then went on with his lecture.
Editing I (Georges Elencwajg) am sorry to have caused some confusion yesterday: not being able to access the library , I gave a reference in the comments which was probably not the intended one! Many readers were very helpful with their comments, in particular Sándor, who took the trouble to copy the text corresponding to my reference and David Roberts who put it here in the answer and which you can read below. Thanks a lot to all.
To quote jstor.org/pss/4145123
"Lance also contributes some new information to the saga of the elusive Mr. Rabinowitsch (see the Editor's Endnotes in the May 2004 issue): Poor Rabinowitsch, whoever he may be. The correct reference is: J. L. Rabinowitsch, "Zum Hilbertschen Nullstellensatz", Math. Ann. 102 (1930), p.520. In various places his first initial is either "A" or "S." On my trip to the library, I saw that Rainich had published in the Annalen under his own name and from Ann Arbor the previous year. Why a pseudonym?" The mystery deepens a bit in a biography of Rainich, where it's mentioned that he was born Rabinowitsch. On the same theme, Herman Roelants of Leuven, Belgium, points out that a Rabinowitsch anecdote similar to the one in the May 2004 MONTHLY is found on page 959 of the MONTHLY paper "Reminiscences of an Octagenarian Mathematican" by L. J. Mordell (November, 1971). Herman goes on to say that details concerning this source, together with references to important number-theoretic work of Rabinowitsch, can be found in the text and in a footnote on page 108 of Richard A. Mollin's book Quadratics (CRC Press, 1996).”