I would say that is a bearing tag for either an aerial survey target for a big game study or it is just a tag marking the edge of a study corridor. The other side of the study is 1254 feet away.
One piece of the puzzle: R5 - 2600 -13 refers to Region 5 (ie California) of the Forest Service. 2600 is the file code for all things Wildlife and Fisheries with USFS. Not sure what the 13 references, might be a Forest identifier.
Transect lines are a way of estimation animal populations. This sign is probably one end of a transect line that runs south for 19 chains. The researcher would follow that line and count any sign of the animals being studied. They would count sign along that line (droppings, rubs etc.) in order to estimate the population.
At least that is my understanding of big game transect lines. Hunting Wife would probably be the authority on this.
Catherine said she has hung signs like that all over the Umatilla and Wallowa Whitman national forests. 1985 was probably a decade before first gen GPS was available so this was a method of being able to find a study area and return at some future date and Survey the area again.