You posted the address 1E6CXTHH15xdyFH7FvhL9TDsb21JWMCpzi in August last year here^[1].
It's the only publicly posted address by your account besides the one in your signature, can you sign from it?

[1] https://bitcointalk.org/index.php?topic=1159185.msg12215396#msg12215396

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That's...not exactly how this works.