OpenStreetMap
There must be another name for these. There has to be a tag for them. They’re so common!
But I see in https://wiki.openstreetmap.org/wiki/Tag:highway=trailhead that a “trail register” is something you might want to tag exists at a trailhead. Yep. How? It doesn’t mention that.
Trying to dig about and find what others have decided on their own. I found some
tourism=information
information=route_marker
name=Trail Register
in New York. In another cluster of two are some
tourism=information
information=board
name=Trail Register
I’ve seen some in the Wind River Range in Wyoming that were built into the information board. I guess it could be an information board with a register. It’s not a route marker. In fact, the one I’m staring at at the moment is at the parking which is somewhat offset from the actual start of the trail. Look, it’s a ridge. There’s room here and the trail is over there. Deal.
In Connecticut, I’ve found a single
tourism=information
information=route_marker
trail_register=yes
so there’s some more support for calling it a route marker. It’s not! It sorta can be. But it’s not!
I’ve found a
tourism=information
information=trail_register
in southern California similarly in Iceland
information=trail_register
man_made=cairn
name=Arnarfellsbrekka
and, I mean, what? I guess maybe a named cairn could have a register. Certainly cairns and peak registers go together. Those are usually a little less official than the registers at trailheads.
I have to admit, this simpler one seems best. I see why people are attracted to putting this down as https://wiki.openstreetmap.org/wiki/Tag:tourism=information since the comments people leave are often the best source for information about the trail conditions you are about to experience. I may have accidentally weighted my search for this tag, though. Not all of it, but the later of it.
So one can do user defined values for information=, one does not have to choose from the small selection in the wiki. I’m going with…
tourism=information
information=trail_register
Unless someone can mention that just ain’t British enough. I sure wouldn’t know. Certainly all but one of the examples I found were in the United States.
Discussion
Comment from SomeoneElse on 4 July 2023 at 09:42
Taginfo suggests there aren’t that many mapped so far, but https://wiki.openstreetmap.org/wiki/Tag:information=trail_register seems sensible to me!
They aren’t as much of a thing in England (though leaving details where you’re staying about where you’re going and when you’re expected back are).
Comment from valhikes on 7 July 2023 at 14:38
@SomeoneElse Yeah, you’re supposed to tell someone when you should be back and where you’re going in between. Some people leaves detailed itineraries in an envelope in the car. (SNR mentioned you can even do a foil print of your shoes so they can track you when they chatted with our Girl Scout troop.) I’m not so good at doing that, so an entry without an out date in a trail register and an apparently abandoned car might be the last anyone ever knows of me.
Looks like information=route_marker has a few more uses. But a trail register as trail marker isn’t directional, so it would really only be information=trail_blaze. (It’s not just for blazed trees! Although pretty sure I’m one of the misusers of this in the past.)
Comment from SomeoneElse on 7 July 2023 at 18:30
Yes, I was surprised to see that “information=route_marker” tends to be used for this (albeit for a few values only), as that doesn’t really match it’s normal meaning. I’d be tempted to make up a new value for these, but like you I’m surprised that other examples in the US aren’t already mapped as something else.