I found some pictures on a public domain website of logos similar to those used on the show, Sons of Anarchy on FX. I have copyright questions.

It doesn't matter where you found the pictures. What matters is whether rights in the pictures can be transferred to you to use them on shirts. I am not sure what you mean by a "public domain website." I assume that you mean a site where photos are offered for "free." Even on those sites, you need to check the license on how the pictures can be used. Also, if you check the fine print, the website has most likely "disclaimed" any liability in case someone might sue you for infringing their rights by your use of the pictures. You know that the pictures are of a show on FX. Almost certainly, the FX show is not allowing people to use their pictures for free. You could check with the show to be sure.