Did you know that benchmarks are part of Geocaching? (see info on this link: https://www.geocaching.com/mark/ )
You can log them and they show up as part of your stats. However they do not add to your overall count.
To log the benchmark you can go to this link: https://www.geocaching.com/mark/details.aspx?PID=JZ3746
So how do you find the log to sign. Well turn around! There is a sign behind you with a historical refernce. Find a series of numbers that begin with 49. Treat the numbers 49.ABC.DEF.
Now do some math:
N39.1.399-ABC and W84 38.648-DEF
You can check your answers for this puzzle on GeoChecker.com.