This snippet from Wikipedia sums up the range of ふだ pretty well:
(very) Roughly translated:
札（ふだ) are paper, wooden, metal etc. things with words, pictures or symbols written on them, such as Hanafuda cards, price tags, slips you can get from shrines, amulets/charms, placards, etc., that convey some kind of information, etc.
(there’s a lot of -たり,など, and やs in there…)
In English, I think what differentiates “tags” most particularly is that it’s attached to something to describe it. A price tag describes an item’s price, a dog tag describes a soldier’s identity, etc. Hence “tagging” something is attaching information to it.
That doesn’t seem to be a necessarily qualifier for 札（ふだ) , so I would hazard (very broadly speaking) all “tags” are probably (some flavor of) 札（ふだ) but not all 札（ふだ) are “tags”
The most ふだ-ish ふだ (in that it’s an お札, as in おふだ) is probably something like this, from a shrine or a temple (I’ve never been so I’m a little foggy on the details):
I don’t know exactly what you would call one of those in English - the wikipedia page is just “Ofuda.” It sounds to me like when you put something like that in a pouch and carry it around, that’s where the “amulet/talisman” type of English translations come from, not necessarily the metal jewelry that may spring to mind from those words in English.
The tag picture Joeni posted is a great example of an English “tag” and would probably be called some kind of ふだ in Japanese.
As an example of a definitely non-tag flavor of ふだ, hanafuda is just 花札.
It seems like さつ in contrast, by the way, is mainly just banknotes (and possibly other official things like proof of licenses for pets, but mainly banknotes).