Transmitting without identifying is illegal in nearly all circumstances.
One exception to this is when you make a transmission of type TEST on a band that allows such. TEST is defined as an unmodulated CW signal (since it is unmodulated, it can't include an ID). TEST is only allowed on HF bands (and a few other areas) where you might use SSB or CW.
In other words, it is legal to tune up on HF without identifying.
But repeater bands (which use FM) do not allow TEST, so you must identify there, and if you key up on FM, it is modulated, even if you don't speak.