Howdy.
It is assumed that since you have chosen to download Bob the Visigoth's Armory, that you do have Better Bodies installed.
Just place these two dds files into your BB textures folder (path is usually Data Files\Textures\BB) and your orcs, both male and female, will be tattooed.
If you only want to have tattooed male or female, just put the appropriate single dds file into the folder.

bb_skinf_or.dds is female
bb_skinm_or.dds is male

Enjoy,
-Mr. Dave