I've been thinking about this a lot. I see only 2 ways to do what I consider a *true* BHS. (Blockheight signature)

1) The BH at the end of the craft is remembered and applied moments later.

Craft is done at 840 005 -> process of marking start -> 840 005 is signed on Block 840 010

2) The BH of the present moment is engraved as soon as it is mined and true.

Craft ends at 839 990 -> process for marking starts (it takes time to setup) -> wait for block 840 000 to be mined-> sign as soon as it is.

The signature is part of the craft. One mistake and it can ruin the piece. As the Artisan, I have the right to decide when I want to finish it. I'm that case I would consider a chosen blockheight to ne a true signature as long as the signature is done when the time is true.

I cannot simply sign the BH you're asking me.