Can you sign a message with an old address of yours?
E.g. 13u8BZVUNcYvVWypPWFA5MUbHJ1YxAC6m3
No I'm sorry I don't remember that address. My main old address is
https://blockchain.info/address/13bwE1rrLnDec67BsSRCg2dubL7qsY5yP2Which you can found here for example
https://bitcointalk.org/index.php?topic=774226.20 - unedited thread.
Edit: here's the message
-----BEGIN BITCOIN SIGNED MESSAGE-----
Hi shorena! This is from dbshck. Today is 9 February 2015.
-----BEGIN SIGNATURE-----
13bwE1rrLnDec67BsSRCg2dubL7qsY5yP2
G1kkl/ql8tUFTZ0zcrzuAWJ+SspWS/Lzm/9IC0oGojfnVBybirmhrOstnf18sTkmoBV/gtQImdYEYTKHm3JRdxw=
-----END BITCOIN SIGNED MESSAGE-----
I ca do it! Please confirm to me!
Confirmed, please send the amount to the BTC address.