At the bottom of all pages, there's a line that says when the current page was last edited. For example, the MediaWiki main page right now has this:

This page was last edited on 3 October 2019, at 09:16.

The problem? There's no indication what timezone that is. I happen to use the default which is UTC. But if it's UTC it should say UTC. But when this is fixed, the person should make sure that it works correctly if the user has chosen different settings in the Time Offsets in user preferences.

Also that comma above seems spurious. My suggestion is that the line be changed such that it would like like

This page was last edited on 3 October 2019 at 09:16 (UTC).

There's still some ambiguity here too over AM or PM but it's far better. I think this is an important matter because without the time zone indicated, there's a "plus or minus 12'ish hours" uncertainty. This causes trouble with printouts, monitoring vandalism, etc.