I'd stress out majorly about mixing them up. I'd have had something done before the name tags came off.
Given how much fussing went on, on a thread a couple of weeks ago, about the toxicity of nail polish, I don't think I'd do that. But given it's a tiny amount, if you're happy with it, then don't stress.
Babies are so good ar removing things, and I'm so paranoid about them choking, I'm not sure I'd relax if I used ribbon/jewellery etc.
Tattoo - I think a single dot on T1 and a double dot on T2 would be fine, just like one of the many many needle tests/jabs babies have. I'm just not sure. Coukd bring myself to permanently mark their perfect , beautiful, baby skin - no matter how inobtrusive
Thank god I didn't have identical twins (I don't have non identical ones either), I think this issue alone would have been the end of me 😅
I think, probably, nail polish is the best answer, but I'd go for all toes in a pale colour. ALL to reduce the possibility of it coming off & pale woukd be enough because as long as somethings there you can tell, you don't need to be able to see it from far off.