15sLQH8je74mcKQDPgVBbSfCAQggSfFXut
Okay, if you don't want to sign it's okay. I quoted it.
Although I don't know how you will prove that you own it later.
if you have another option i could use, then i would be glad to welcome it, the few wallets i know do not give me that option either.
Export the private key(seed) and import it in Electrum then you can sign a message.
Use this as a guide :
I don't actually have the seed orelse I would have simply imported the address and signed a message from blockchain wallet itself.
The only things I have is: "Wallet-id & password" which gives me access to the blockchain wallet.
I hope the email verification works as it's my last hope perhaps.
This is enough, login to your blockchain wallet, go to Secuity Settings and then Backup Phrase.
Click on the Backup Funds and follow the instructions.
There you gonna get your 12 word seed which you can import in Electrum.
It's easy.
I even made a guide, see below