like most of us, i have tried many kinds of marks for the bottom.
the one i find best is made by Mayco  and is a silkscreen.
computer generated, you use some colored slip to put your name
on the bottom through the stencil. the problem with metal stamps for
me was that the surface needed to be pretty flat and the clay the
proper consistency for the stamp to show well.   They are very inexpensive
and can be sized any way you want.  they come on an 11 x 8 sheet, and
last for a long time.
Gregg Lindsley
Earth and Fire Pottery
10325 Brookside Drive
Middletown, Ca. 95461

Function and Beauty
in the Mingei  and
Bauhaus traditions
'At home among the lost and found'