I think that's a question Sypha's better equipped to answer than I am. Typically it requires some sort of personal connection, as I understand it, with locks of hair being quite common.

[Alucard still doesn't like it, having to act as a perpetual eye over a single man. But it's for a much greater good and preservation of life, so he can't argue it. Not really.]

I hope that traveling helps, honestly. Staying still is likely to let things fester right now.