On folio 1r in the codex I.6.2°.5 of the Universitätsbibliothek Augsburg we find a date by a year number “1491” and the title “Memmorj der Maister dess Lanngen schwerts jnn Franckffurt etc.” (“chronicle of the Masters of the Long Sword in Frankfurt”). But the most remarkable is the symbol on this page, which looks like a very special key (link to the image: http://media.bibliothek.uni-augsburg.de/fullsize?id=47520).
This book was copied around 1566 in commission of Paulus Hector Mair, thus we cannot be sure that everything in this book is according to the original. For this some further research is needed in the archives of Frankfurt. Until now to me an other usage of that symbol is unknown.
The interpretation of such symbols is often nothing more than an educated guess. There is in this context the obvious connection to the five secret strikes (Zorn, Krump, Twer, Schieler, Schaitler) a Master of the Longsword must be ready to present to become a master according to the rules set in the same codex.
Zum Ersten Soll jn der haubtman versuchen jn dem schwert vnnd jn der 5 verborgne hawe Erforschen
Those strikes are the basement of the 6 techniques called the master-strikes, tested by the masters of the brotherhood. Depending on the interpretation of the strikes themself (how those strikes are organized and executed) the solution to read the symbol differs. The reading of the symbol may allow us the additional theory that there are three lines of height defined: head, shoulder, and hip. What may be displayed by the three crossings of the center line. The author of this blog does not want to dive to deep in speculations but invite the reader to find her/his own reading of the symbol.