Query: "I've got your number."

[Gerald Cohen]

 A colleague has asked me about the origin of the slang phrase "I've got
your number" (= to have precise, useful knowledge of someone's weaknesses;
have someone in a critical position).

I checked Jonathan Lighter's excellent HDAS and see examples going back to
1853, but I don't see an etymology given, so I suppose this silence equates
to "Origin unknown."

I see various items on the expression in Google but am not clear about their
reliability.  Would anyone know what the "number" originally referred to?

Gerald Cohen

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