I'm not a huge fan of those tatoos but at least they're more feminine than some of the otherwise attractive women I know with full sleeves. There's one woman in particular, a good friend of mine, as sweet as can be, that has these weird, hideous circles all over her arm. I don't know if they're supposed to be alien heads or what.
"There was just a shot where you got a brief glimpse of the tattoo on Charisma's lower back. This was edited as much as we could, I believe, so that you couldn't see it. Because it was generally felt that that would not be something that Cordelia would have, would be that tattoo. So it's generally hidden, every now and then you get a glimpse of it." - Jane Espenson on the commentary for Rm w/a Vu (Time Code on R1 DVD: 35:37 - 38:00).
- Michael, bored transcriber.
Weird, because I'd think it might be something Cordelia would have. Maybe not but it's not totally out of character.
As for Willow, I certainly wouldn't expect to see any tatoos on Willow during Seasons 1-4. But after that, I could see her & Tara getting really crazy in some kind of stereotypical lesbian rebellion. More likely though, it would have been Kennedy's idea.
As for the other ladies on the show:
Buffy- I don't think so. If she did, I think an episode would have outright mentioned it.
Anya- No, unless that's what she thought Xander wanted.
Dawn- I think she'd want one but I can't see Buffy or Joyce letting her get one.
Jenny Calendar- I hope so!

(Anything to make her seem kinkier.)
Faith- Pretty much a requirement.
Fred- No way.
Eve- She seems like the type. After all, she went to UC-Santa Cruz.
Darla, Drusilla, Lilah- Sure. Why not?