With guitarists, it comes from their fingers and “rig”, but, mostly their fingers. Same for bass. I would say maybe for all stringed instruments. I can pick out Jimi Hendrix or Stevie Ray Vaughn in a heartbeat.

Synths are somewhat tougher. Of course, the more expressive the synth, the more likely someone’s signature sound may emerge, ala Vangelis and the CS-80. I wouldn’t say Darryl Hall and his Prophet-5 created a signature sound though, beyond his music sensibilities I mean. But, sonic cues like playing and performance styles, composition and arrangement styles, along with specific genre and influence cues, can help identify who’s behind those keys, if it’s a blind test! Emerson, Wakeman, Hancock, etc.

Piano has a lot of expressivity as well, but one needs to spend time immersed in the music to appreciate the differences, imo.

Saxophone, Tumpet... those woodwinds and horns are very expressive, like voice extensions... some jazz guys had very signature sounds. Parker, Miles, etc.

A Hammond B3 has a lot of expressivity, so greats like Jimmy Smith to Jon Lord had very signature sounds.

Drums, same deal, but in a cool and different way. So many (fairly) identifiable greats. Thinking Bonham, Moon, etc.

We each absorb influences and when expressing ourselves over time, our own style naturally emerges, like it did for those mentioned above.

But, if a tree falls in the forest and nobody’s there to hear it, does it make a signature sound? What if all the trees are falling at the same time?

I guess what I’m saying is, just be yourself, have fun, and work persistently on your craft. Let the sonic signature chips fall where they may.