I am so happy you guys take out the time and write such detailed information. It helps us understand so much. Shout out to all people who take out the time to help others!

Are there online wallets with signature messages?

Verified OK! That all checks out

excuse me for my noobness questions, but what is the purpose of this sign message? why you have to do a sign message if there a few wallet has no feature for it?

Sorry... this doesn't verify...

I think you've not posted your message properly... it should be like this one, without all the <>'s:

-----BEGIN BITCOIN SIGNED MESSAGE-----
S_Natural bitcointalk 2017/09/05
-----BEGIN SIGNATURE-----
176rVybXv6T7X4RaY6iyBQt1MBwVrpTc5B
IHpDE3QbiOf05k+FVIutzeoVG2HeG6YRYT/rZSt3adgoAZdt8OUkfV7pG6MEcx/dwmn5jkmiy1ftjhjYtDigl+w=
-----END BITCOIN SIGNED MESSAGE-----

I use poloniex address. I have slow internet and really not a tech type guy. Is it possible to sign a message using exchange BTC address? I have no control on private key, right? So, is it possible to sign a btc message ?

You can't sign a message from exchange btc address, because it's in control of excange and you don't own this address.
If you have slow internet and you don't want to download any software, you can easily sign message from Blockchain.info wallet address, just follow tutorial.

-----BEGIN BITCOIN SIGNED MESSAGE-----
This is cryptme, bitcointalk.org user 843342
I sign this message to recover my account in case is compromised.
Today is the 6-th of october 2017 15:02 GMT+2
-----BEGIN SIGNATURE-----
1MYiHNHjyNrdSHaZoRLn2Na7bjh86de5ir
H/9rdGtjzDGeMBmQJFjzT9OzSTcuXtAREsyRQuEGQ160JbTzazUou7JX4xiz6oBIMrMdJy0icUjiQPyRgDnVFXU=
-----END BITCOIN SIGNED MESSAGE-----

how about u dont have a bitcoin sign msg.? u can retrieve my stolen account? my account was hacked by yesterday i want to request that i already pm to theymos.

Message failed to verify! Check again man.