I like both my career at FedEx and my tattoos so suffering long sleeves in August is worthwhile. Your thread prompted me to do more digging. While there’s nothing on PFC and nothing in the FOM regarding specifically tattoos, I was able to find the following in “the People Manual”, section 2-80.
“Visible tattoos, gauges exceeding half an inch with a flesh colored plug, and/or body/facial piercings, except for an earring in one or both ears, are normally prohibited in customer contact positions when wearing the appropriate Company-issued uniform”.

I’m sure that can be jail house lawyered, but I’ll just keep my long sleeves on and a sweat towel handy if I’m ever jumpseating you’ll probably see my art.