On occasion I've seen a novel in which the writer wants to identify a year by all but the last digit, so that the year could be any year in a decade. I want to be certain of the punctuation mark that would be used under such circumstances. It could possibly be 198_ or 198- or something similar (en or em dash.) Wikipedia doesn't address this.
There are multiple ways to do this. TVTropes has plenty of examples.
Some works use an em dash:
On a fine May day in 197—, Fred Regent and Richard Jeperson stood in Old Compton Street, London N1.
Soho Golem by Kim Newman
Another way (very popular in video games) is to use X:
The year is 199X — Earthbound
The Oxford English Dictionary uses periods (e.g. "14.." for the 1400s or "187." for the 1870s), which is something I haven't seen used anywhere else, especially since it would be confusing when written in a sentence. Still, it's worth mentioning. Here are some screenshots from their page for up (adverb):