This symbol was "adopted" from the existing ISO 9573 standard which defined entities for use with SGML. It appeared in the entity set ISOAMSA, which, regardless of the name, had no connection with the American Mathematical Society; instead, it means "added math symbols", as evident in this listing. I had no idea what the symbol meant or was used for, thus assigned it a "descriptive name" when collating the symbols for the STIX project. (I still have no idea, nor can supply an example of the symbol in use.)
A rather unwieldy position-specific table containing information on the collection submitted for consideration by Unicode can be found via links on the web page https://www.ams.org/STIX ; this is not the final table, which was updated after Unicode assignments were made, but I was pulled from the project before I could complete the tidying up. I am now retired from AMS, and no longer have access to the paper records used to compile the collection; those were left with the intention that they be properly archived, but I have no knowledge of what may have happened to them since.
Paying more attention to the information provided in the question, it is the case that ISO 9573-13 existed long before either AFII or the STIX project were formed. 9573 was an adjunct to the SGML standard, compiled by the same or associated people. I once asked Charles Goldfarb what the source of these entities was, but remember that he didn't have a definitive answer.
Addendum
Even though this question is now closed, there's more useful information available. The OP has done some heroic archaeology, and found among archives holding Monotype punches the actual punch used for producing type for this symbol. A photo of the punch is included in this blog entry. It may have been a special order. The shape differs from the one currently shown in the Unicode charts (I'm going to try to get that fixed), but it's indubitably the same symbol. And we know by this that it appeared in print at one time. But the meaning is still not known.
