Very useful thread , my address below which is registered with Bitgo as :
Address : 35aivb3buhXfSkSkdnZ4HnYgivhuh1qxR8
PBG :
BitGo Public Key
This is the public half of the key BitGo has generated for this wallet.
Data:
xpub661MyMwAqRbcGaXLC61oNQqAkTyXbLuwzT2Xb76wJ1DVSLq1hWh5jZzbXN4aFnou6G92qUp
BatpzfuSP5rD3QruYFSnf8Quf4QTaUnmAro1
Thank you
Don't know what to say for this, it's not an address that you can sign a message from it?
Maybe you can prove the ownership but I will hear others what they think about this!
The address (multi sig) cant be used, true. Technically its possible, but there is no clear standard how to do it (e.g. are 2 out of 3 enough if 2 out of 3 are enough to transfer funds?).
The xpub however would reveal enough regular addresses for the user to sign a message with.
Edit: here are the first 5 according to electrum:
#1 1DMRPDYn3t9G12WTasKZiF2XPK7K4bKpgL
#2 1Eqn6ynajP7gmrckFdJusmmk1Gib5e4gik
#3 1Q9j4895C1aNCmMHEmr5BrV8Gn42SCin7m
#4 1gTfJh4QrzRWThbwA5x8ttucBoErXMz5y
#5 1NaWCR8eLszTYgEDvQ3mBowkAMDwiYxnJc