This is the somewhat overbuilt signpost for Michigan highway M-115, which has one end in central lower Michigan and continues to the northwest where it ends at this sign.
The highway was originally earthen pavement when first constructed in 1929, but by the mid-30s the state was repaving the existing sections with asphalt and extending the highway with gravel as well.
There is no description on the back of this card. The auto in the picture, along with the initial construction date, indicate that this photo is from the 1930s.