Designed by Witold Chylewski, this was only the second pistol manufactured by SIG (the first being the 6.5mm blow-forward 1894 MAnnlicher design). It was patented prior to WW1, but only after the war was Chylewski able to find a manufacturer interested in his gun. The most notable element of the design is the use of a sliding trigger guard to allow the pistol to be cocked using the trigger finger, thus allowing carry with the chamber empty but still able to be drawn and fired one-handed. The pistol was chambered for .25 ACP (6.35mm Browning), and had a 7-round magazine.
SIG contracted to produce 1000 of them on license, but seems to have been unable to sell them all. Chylewski later took the patents to the Lignose company, where they formed the basis of a series of “Einhand” pistols in both .25 and .32 caliber, which were more successful (and as a result, more commonly found today).