Bitcoin Forum

This thread is targeted at newbies but higher rank members can find this helpful too.

What is a signed message?

Message signing is a way you prove you are the owner of the Bitcoin wallet and have control of it.

Advantages of sign a message on bitcoin talk.

The major function of message signing is to prove the owner of an address, either to prove a transaction by signing a message using the wallet address, But on the bitcointalk forum, there are few other advantages of sign messages.
1: it helps recover your Bitcointalk account in case of a hack/stolen account if you stake your wallet by signing a message from it and posting it on this thread.https://bitcointalk.org/index.php?topic=996318.
2:To encourage and appreciate your sign message skills you get merited by a reputable member of this forum.https://bitcointalk.org/index.php?topic=5300698.0Hope you find them helpful.

It would be more correct if you say "prove the ownership of one bitcoin address". To sign a bitcoin message, from one public address you must to have an access (control) of its private key.

With one private key, you can import it and sign a message in different bitcoin wallets as long as they support the type of address you are using.

You are right that signing a message is useful for the things that you have mentioned like recovering your bitcointalk account and also as a proof that you are the rightful owner of the address. For learning how to sign a message, there is a respective thread for those who don't know how to sign can read and then learn. Nust visit this thread https://bitcointalk.org/index.php?topic=990345.0

Digital signatures are mainly used to prove both the authenticity and the integrity of the signed message/file. It proves that the received message was really written by whoever signed it and that its content hasn't been tampered with.
It's mostly used when communicating/transmitting data over some unreliable transmission mediums/protocols.

You might want to check out the thread "How to sign a message?! (https://bitcointalk.org/index.php?topic=990345.0)" by shorena before you go and try to reinvent the wheel (or the thread as the case may be) over in the Beginners and Help (https://bitcointalk.org/index.php?board=39.0) section of the Forum.

This is not a long term benefits, of sign message, since the merit is given once, it's really benevolence of the merit donor doing this, but the reality of the intention is like you said an encouragement, but many Newbies only aspire give the merit in the offering.

I think a sign message or the knowledge of it is a necessity for in-forum and off-forum Bitcoin-er, but many aren't knowledgeable about this necessity, I actually experienced difficulty try to sign a message from my mobile phone, till I tried it on my Laptop.

There is nothing hard to sign a message using mobile wallet, mycelium wallet can sign a message, coinomi can sign a message (but coinomi is close source which is the reason I do not recommend the wallet). Electrum can sign a message too, but only on desktop versions, its mobile versions do not support message signing even in the latest release.

Which mobile wallet did you use?

If it is electrum, it can not yet sign a message, only the desktop can for now. 

If anyone want to sign a message on mobile, please consider a plain, empty wallet just to sign a message.
If you don't need to sign it and at the same time need to show proof that address has some Bitcoin for trade deal, an emtpy wallet on mobile is fine.

On mobile, you have risks of loss your phone,broken device, and malicious things. Those risks are reasons I recommended an empty wallet on mobile.