I was asked by Bittrex to send a signed message from some previously used wallet... and in my case I only sent something from Poloniex to there....
Can please someone tell me if it´s possible to send this signed message (deposit with some specific message) from Poloniex?
Unfortunately, that's not going to happen. I don't believe they do this for customers; they simply can't at their scale. And it would probably introduce security holes into their protocols if they did this for customers using their hot wallet. You can try contacting Poloniex, but you'll probably wait a month just to have them say they won't do it.
Would you mind saying why they asked for this? Did they disable your account?