From the NPS link:

Letterboxing involves the placement of a cache containing a stamp and an inkpad that enables participants to document that they found the specific location. Participants find the location by following “clues.” Clues often involve map coordinates or compass bearings, but most letterboxes currently in existence do not require the use of a GPS device. Although letterboxing is intended to be environmentally friendly, if the “box” is buried or concealed by manipulated vegetation or rocks, or will cause participants to create social trails or traverse sensitive or dangerous locations, the impacts will likely be unacceptable. However, it is entirely possible that some parks, particularly those with a vast expanse of backcountry, will have locations where a letterbox could be concealed and sought out without causing unacceptable impacts. In those cases, the superintendent has the option to designate locations where, or establish conditions under which, the cache could be left unattended—for example, in the same location as an NPS- sponsored summit log.

So the answer to the OP seems to be no, don’t automatically assume a letterbox in a National Forest is placed illegally.

So the answer to the OP seems to be no, don’t automatically assume a letterbox in a National Forest is placed illegally.

Actually this link and your quote only applies to National Parks. Department of the Interior.

National Forests are Department of Agriculture which has never had a ban.

But essentially it is like many other state and local parks, whether the box is allowed is officially up to the park manager, if you choose to ask them.

As a general rule in my travels is I do not plant on NP property, though as some of you who have found my NP themed boxes they may be right over the boundary line (Zion, Bryce, Capitol reef, fossil butte) and some of those you have to drive through he NP to get to non-NP public land. I have found a few boxes on NP property but I doubt they were placed there with permission. Only one in CO, was at the visitor center and you had to ask a ranger. As eidolon said, you would need permission from the park manager otherwise.

I did not find this to be the same in Canada parks though.

What are Canadian rules?

So I couldn’t find anything specific to letterboxing but here are the geocaching rules. Similar, but in my opinion a little more liberal than the US National Park regulations, or that just may be my interpretation, but I’m not a lawyer, I’m a dawgdok.

https://www.pc.gc.ca/en/docs/pc/guide/geocache

I've been boxing for 12 years, and have always gone by the philosophy of "what they don't know wont hurt them."

As long as the box was just off a trail, or in a safe area I would look for it . . . heck, I'd even plant one there (have to make sure the clues are cryptic enough not to pop up on their searches).

However, if a box is WAY off the path, in an unsafe/fragile area, I'd stay away.

hx6

Thanks! This is a very educational topic!