Segwit addresses cannot sign messages. This is one of cons pointed out ranochigo.
Well, it can sign messages, but there is no standard to recognize it. In practice, you cannot sign a message from segwit addresses which will be recognized by all software.
But you can with Legacy. A message signed from a legacy address will be recognized everywhere.
I do not think this is an issue if there are lot of software to sign segwit message, any wallet that support segwit and that can verify message will support segwit, I have used electrum and coinomi for this before, there are still some wallets like that, I will soon the one for mycelium, and I believe it will be able to verify segwit messages.