It was placed as part of Pi day, March 14 (3.1415 or 3/14/15). To figure the actual location you will either have to research some information or walk/drive around Mackinaw City for the answers. Then simply fill in the blanks. The final location will be:
N 45 46. A B C
W 084 43. D E F
Now for the clues:
A. Find the Star Line Ferry dock in Mackinaw City. Look for the address (three digits). Add all three digits together and your sum will fill in letter A.
B. Find the Wa-Watam Township Hall. At the building you will see the year that the building was built on the top front of the building. Subtract the year of establishment from the sign in front of the building from the year the building was built.
C. Somewhere in town you will find a building with a giant 60 foot long, seven ton Hot Dog on top of it. It has been entered for the Guinness Book of World Records. Find the address of this establishment. This may take a little additional research. Once you have determined the address, add all three digits in the address together. The sum will be you answer for Letter C.
D. Look for the American Legion Post in town. Out front you will find the Post Number (not the address). What is the last digit of this American Legion Post Number. This last digit will be 'D'.
E. The original Coast Guard Cutter Mackinaw now resides in Mackinaw City and is a museum with tours available in the summer. She shouldn't be too hard to locate, look for the big red ship. Determine her two digit hull number. Subtract the second digit from the first and this will be 'E'.
F. Somewhere in town is the Great Lakes Lighthouse Keepers Association. Determine the address of that location (three digits). Take the first digit and add the number two it it. This will be 'F'.
Good luck and happy hunting.
You can check your answers for this puzzle on GeoChecker.com.