In jusletter.ch, Corinne Zellweger-Gutknecht argues that the legal status of central bank reserves is more equity- than debt-like—at least as far as the Swiss National Bank (SNB) is concerned. According to Zellweger-Gutknecht, reserves constitute debt only if the SNB is legally obliged to redeem them in exchange for central bank assets.
If the SNB purchases dollars against Swiss Francs in an open market operation, it creates reserves which are equity-like. But if it acquires dollars against Swiss Francs and is committed to engage in a reverse transaction in the future (a swap), then it (temporarily) creates reserves which are debt-like.