[Along with a delivery of medical supplies is a little something for Sam as well. Huge sacks of flour, sugar and chocolate for his baking needs, but that's more for the clinic than anything. So there's also a thumb ring. But those aren't jewels, rather, it's Jekyll's own blood crystalised. A note explains.]

Dear Sam,

Happy Christmas and Yuletide, I hope you remember to take as much care of yourself as you do others.
This ring will allow you to call for me, for any reason. I will be alerted and able to find just where you are if you simply press upon the stones.

Your loyal friend,
Henry

[The way he'll be alerted is that his own thumb will bleed of its own accord, but, no need to mention that part.]