Bonesaw is similar to mechanic’s wrench. They are both single handed melee tool-items. And both will let you do yourself damage, potentially. Vincent's weapon has an updated, better version of the Kukri effect. If he wants to, he can do an extra damage, trigger bandages or Jessica Hyde, then slash again with a fresh On the Mend. Kind of a dark mirror to the meat cleaver.

The secondary effect feels like an emergency button; there are very few effects in the game that can reduce that much damage on someone, especially if you’re healing people steadily to give them On the Mend. Combining that test with premonition, neither rain nor snow, or other downside mitigators is best. If your allies have trauma, it should be because of 'in the thick of it'.

Since it’s a tool, it can go back in your Tool Belt when there’s nobody around to stab. Situationally very useful, which is the sweet spot for a signature card.

Not a distinguished combo but I wanna point out that even in a non-fighter Vincent deck the sawbones' tool is still a good synergy: it's usually better to play a signature than just commit it into skill test, however since Vincent is access to Scavenging, it's possible for a cluver doctor to commit his surgical garget to a test and recur it back for the next one, transfer the card into another Perception every round without extra draw. Also it has a Tool trait, so Crafty helps comprehensively on playing it and the skill boost for its fight and healing action.