Who do you build the Talisman on?

Soraka, Janna, Thresh (sometimes). There aren't many supports than can actually utilize the Coin, and most of them just use Edge better, except Raka, Janna (though I still see her building Edge so maybe Im wrong?), and Thresh. EDIT Also Alistar uses the Coing pretty alright, but usually I would rather just build Shield.

Making a short list:

(If you're not good at last hitting or you just sick of having for the last hitting minigame.)

(Because armor for his abilities.)

Janna is good with spellthief/eye of the watchers because most her abilities, including the utility ones, have pretty decent AP scaling. Soraka almost sits in the same boat (though she can really go for either eye of the watchers or eye of the oasis), with her w having a .6 AP scaling (so if you play it safe and make sure to land Q regularly, the extra AP actually makes your healing more efficient). Thresh would be fine with coin except for the part that he's a tank and his base stats have been nerfed a lot (which makes him kind of need the extra health from relic shield/eye of the equinox). Taric really benefits from the health from relic items to back up his armor more than he benefits from anything he'd get from Talisman aside from mana regen if you need to use starlight's touch a lot. Right now I'd say that Talisman is still pretty situational and even the ones who can use it still usually gain more from a sightstone upgrade that instantly gives you 4 wards, better slot efficiency, and allows you to more quickly buy other items your team will want you to have (like Locket).