By default all Tryst profiles have Tryst messaging enabled, which allows clients to contact you using their Tryst account. If you don't want to receive messages via Tryst, you can opt out by disabling the contact form on your profile.
Log into Tryst and go to your Dashboard. Click edit profile and then edit Contact Details. Check the "Disable contact form" checkbox and save your changes. The Message Me button will be removed from your profile.