If you're interested in a real simple --and cheap-- option, here's what I did.

First as a "mark" I have always used a simple "monogram" consisting of
a combination of my wife's and my initials in a "plus-sign" pattern.
(Which, needless to say, greatly simplifies what I need to do.)

Anyway, I got an inexpensive set of letter-punches.   I then made a 
wooden sleeve
which holds the right combination of letters in the correct 
arrangement.   Then place
the contraption on the wood, and a light tap with a hammer makes the 
impression.

As I say, what I was needed was pretty simple.  But this setup more than
does the job for me.

Hope it helps,
Nichael 

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