No, there are not “exactly 3 ways” to specify the ‘magic comment’ — there are an infinite number of them. Any comment on the first line that contains coding: will work, according to JEG2:
… the preferred way to set your source Encoding … it’s called a magic comment. If the first line of your code is a comment that includes the word coding, followed by a colon and space, and then an Encoding name, the source Encoding for that file is changed to the indicated Encoding.
So, any of these should work:
# coding: UTF-8
# encoding: UTF-8
# zencoding: UTF-8
# vocoding: UTF-8
# fun coding: UTF-8
# decoding: UTF-8
# 863280148705622662 coding: UTF-8 0072364213
# It was the night before Christmas and all through the house, not a creature was coding: UTF-8, not even with a mouse.