this is the entrance to sanford community forest, a conservation area owned by Three Rivers Land Trust. To verify, check CIty of Sanford property records.
https://www.axisgis.com/SanfordME/fOH0FjXLkINM

please identify Sanford Community Forest, owned by Three Rivers Land Trust, as conservation land. On the City of Sanford's tax maps, it is identified as R4-23.