So normally the area around the UW football stadium in Seattle has these rather unique parking signs that use decals that are stuck on each year that list specific dates and times when parking is prohibited that coincide with that season's schedule for home Huskies football games: https://goo.gl/maps/EoLLePmAgkf7ctYn7
But a couple weeks ago while on a bike ride I noticed that this past year a special decal was applied that simply states "no sports or event parking restrictions until further notice", which a rather bittersweet anomaly.

As this was just mentioned recently, I went back to the sign in qn.
Despite the slighlty ambiguous language, I can clearly see that this sign was meant to restrict access to parking during stadium events, unless you have a zone 1 permit. Under normal circumstances, of course, there are regularly scheduled football games and perhaps other events (maybe graduation) where the circumstances would apply. I think the university does a nice thing by actually posting the schedule right on the sign for the benefit of those who may not be familiar with the schedule.
During COVID, (or perhaps during the football off-season) a lot of the regularly scheduled events have been cancelled. So instead of leaving the sign blank (basically telling parkers that you are on your own regarding finding out what is being scheduled at the stadium) they are telling you that there is no scheduled events any time soon, so the parking restriction simply does not apply.
Of course, the green sign above, with a 2 hour restriction from 7AM - 10 PM would still apply, even if the stadium-specific restrictions do not.
I wish something like this was done more. There are plenty of parking signs of ambiguous duration, and it is not always well known if the restrictions apply currently. "School hours" is a hard one, because if you park near a school but are otherwise unconnected to it, do you really know the full schedule and understand which days are OK to park and which days aren't. Another aspect is to know which holidays would be exempt from parking restrictions. Practically everywhere the big holidays like Christmas and Thanksgiving would be exempt from these restrictions (unless the restrictions were "all times" or "every day"), but what about a day like today (MLK day). As most businesses are open and most people do work today, there is a good argument for normal parking restrictions, although I do know of a lot of places that exempt street cleaning and parking meters today.
So I like the idea of posting a specific schedule right on the sign. Another acceptable means, IMO, would be a website link that is direct and specific to the parking restrictions. Even though websites are not normally allowed on road signs, to prevent using internet while driving, I'd make an exception for parking signs, since a person can stop, check the website, and then continue driving if needed. Heck, so many places with parking meters allow for parkmobile (or similar apps) that basically using internet while parking on the street is becoming a pretty regular thing anyway.