Sorry for Bumping up the old thread. I was here because I didn't have any idea about how this works. I have learned how to sign a message from my own wallet.
I have found that Blocktrail has announced their service ended in 2019, But, This thread wasn't updated. The thread creator is not active for a long time now. Since this thread is very useful for newbies (Even for some hybrid Sr. members like me

), I think I am doing right by Bumping up this thread.
OP didn't active for 2 years so he can't moderate it, the possibility to edit and change the thread is a moderator.
but, when I read up the thread it's just for verifying messages, which show how to which the same what another wallet did. So, I think it can be continued by using another website in the same way.