Vandals sprawled graffiti - including offensive language - on the side of Boston Stump over the bank holiday weekend.
The graffiti, written on St Botolph’s Church, uses a four letter expletive against what it decsribes as ‘religion and the system’.
A spokesman for Lincolnshire Police confirmed they were investigating the incident.
They said enquiries and CCTV reviews were ongoing.
Anyone who saw anything, or who has further information is asked to call Lincolnshire Police on the non-emergency 101 number quoting incident 136 of August 28.