Long time lurker, first time poster.
I just bought a pork shoulder, and there's a livestock tattoo on the skin. Do folks just discard that portion of the skin?
Welcome to the forum!! Sounds to me like its probably a USDA inspection mark, as most hogs are not branded or tattooed for id purposes. It is up to you weather as to eat it or not, should be food safe ink. Don't for get to swing on over to the Roll Call section so we can welcome you properly !!
I imagine it is an inspector mark. Should be food safe ink as stated. I sometimes see stamps on the fat side of beef primals. Usually the meat cutter will trim it off if he sees it, just doesn't look appealing to the customer and saves time explaining.
Do you have a picture of the tattoo? Is it an actual tattoo (ink needled into the skin) or is it a stamp on the skin?
By law, primals cut from inspected carcasses need to carry the USDA mark. When the packer breaks a carcass with the intention of selling the primals (as opposed to further processing in house), each primal is stamped in blue (sometimes purplish-blue) with the USDA stamp from that house. (in the case of pork, each ham, belly, loin and shoulder receives a stamp). The plant I worked in would occasionally sell an entire head, and we had stamp each on on the forehead.
This ink is edible, although not necessarily desirable. It can look unappealing and can stain surfaces and meat that it comes in contact with.
Tattooing of livestock was a commonplace procedure done years ago, and while it is not common, it is still done by certain producers. It will be black in color, usually consist of numbers and/or letters, and will appear as several dots composing the letter/number.
Although there shouldn't be any harm in leaving this in place, again, it's not necessarily desirable.
The only way to remove either mark is to remove the skin containing said mark.