Not quite. There are two speeds in relativity: the maximum speed and non-maximum speeds (i.e. everything else). It just so happens that light travels at the maximum speed.

Supra-luminal signals will almost necessarily imply that it's possible to violate causality by arranging a series of supra-luminal communications. Not every supra-luminal communication violates causality, but it's hard to think of a way to build a consistent theory that would both preclude causality violations and permit at least some supra-luminal signaling.