In class years and decades, the apostrophe should point to the left:
’02, P’00, GP’89
’80s, ’20s
Note: An apostrophe is the mark to be used here. According to Chicago Manual of Style Q&A online: “In word-processed documents, when apostrophes are preceded by a space (as opposed to those in the middle of a word, like it’s), the software thinks the writer wants an opening quotation mark and supplies one. When documents aren’t proofread carefully, these marks appear in place of apostrophes.”
Avoid using “daggers”: A dagger is a straight, pointed character that can be used as a reference mark or to indicate a death date:
Not OK: '80
How to make a left-facing apostrophe: This character is located in Microsoft Word’s “insert” menu > symbols > normal text > special characters. Select the single closing quote. PC users, creating a shortcut is helpful if you use the character often.
Mac shortcut: shift + option + right bracket key
There is no apostrophe in a range of dates:
1985–89