A photo provided to FOX 5 shows several words written in gold paint on the window.
Santos released a statement about the vandalism, saying "This act of cowardly behavior is beyond unacceptable and compromises the safety of my staff as well as my constituents."
Santos is asking anyone who may know anything about it to contact the police.
So far, police have not released any descriptions of a suspect and no arrests have been made.
Earlier this week, Santos announced that he would be temporarily stepping down from his two congressional committees until all of his issues are resolved.
Santos has very little support in the district he represents. According to a Newsday/Siena poll, 78% of constituents want him to resign and 75% said he could not be an effective representative.