My university has a bunch of informational plaques in front of different buildings. They aren’t in memory of anyone, so they obviously aren’t memorials, but there is no plaque tag under informational. I do see informational board as a category, but the photo reference I see on the wiki is much different from the simple text on metal I have here. I will use informational board as the category for now, but just want to ask aloud in case there is a different category I should use.
In OSM you can use pretty much any value you like, but obviously it’s best if people try and use the same values for the same things. You can see the values used for “information” at https://taginfo.openstreetmap.org/keys/information#values . There are 96 “information=plaque” used worldwide, far fewer than the 151,719 “information=board”. I suspect that a lot of people have mapped plaques like yours as boards because they’re “nearly the same thing”. You can see the plaques that have been mapped at https://overpass-turbo.eu/s/LOQ . If you think that your plaque is like those, I’d use that as a value; otherwise I’d use “board”.