Without trying to turn this into a full "Where is Assange?" discussion, unless the conspiracy against Assange involves compromising such disparate actors as Ecuadorean embassy staff and prosecutor, the Swedish prosecutor, his own legal team, Wikileaks staff posting press releases in his name, Pamela Anderson and John Pilger, all of whom have communicated with him since his supposed disappearance, it's probably safe to assume that he has other priorities than sending a signed "I'm fine" message, particularly since it's already been documented that his preferred method of internet access was cut.