Do you want your $5k bass signed?

[Larchi]

To me, it's like a beautiful piece of art with a little ugly graffiti on the edge.

I agree, though on the back, can be fine. If done right.
On my Dingwall NG3, it just has a Nolly sig stamped on the back electronics plate - it's nicely done. It only has Combustion on the headstock, like normal.
I don't require Nolly or Sheldon to scribble on it.

 

[Old Blastard]

I have two customs built by Andrew Drake. His signauture is on the headstock -- his logo. If I bought a custom from a bigger boutique maker, unless the person themself made the instrument, I'd probably pass. If it was somewhere like the back of the headstock and it was a thing they did, I'm not sure I'd care as long as the instrument was great.