Katakana, Hiragana, or Kanji Name?

If I am a foreigner with a Japanese name, when writing my name in Japanese, would I use Katakana, Hiragana, or Kanji?

It's your name, so it is up to you to decide how to express it. For reference, you may wish to consult with the person who named you (like your parent) on what your name meant or how to write it.

Romaji is also one way of "Japanese writing systems." So writing out (if your name as it appears here IS your name) "Sayaka" is fine. Since katakana is the writing style to represent imported words, you could use that as well, サヤカ. But you'd need to ask your parents or whoever who gave you that name to ask about the background :) Maybe they meant it in hiragana, or there might be some kanji behind it (unless you KNOW which kanji it is that they gave you for your name, you wouldn't usually be writing it in kanji).

Just as the English spelling for a name is different for each name and can't be misspelled, typically there is only one correct way to write your name in kanji. If you know the correct kanji to use for your specific name, write that. That is what Japanese adults typically do. You don't have to know the background of your name or anything.

But of course, just as you are often asked to write English names in block letters instead of cursive writing, sometimes you are required to write your name in katakana or hiragana just so that it can be read correctly.

Hope it helps.

Context matters. For casual usage among your family and friends, romaji, katakana, hiragana or kanji are all acceptable, though if you use kanji you should use the ones your parents have chosen. For official purposes, different rules exist depending on the particular context, but typically unless you have Japanese citizenship and a koseki, you don't really have a Japanese name (just one that sounds like one) and it will generally be written in romaji (or in katakana in cases where romaji is not acceptable).