PS vs notation

PS and notation both are nouns.

Word	Noun	Adjective	Verb	Adverb
PS	Yes	No	No	No
notation	Yes	No	No	No

As nouns, notation is a hypernym of PS; that is, notation is a word with a broader meaning than PS:

Other hypernyms of PS include annotation, note.

PS (noun)	notation (noun)
a note appended to a letter after the signature	the activity of representing something by a special system of marks or characters
	a technical system of symbols used to represent special things
	a comment or instruction (usually added)