Windows have been vandalised at the front of the Shakespeare's Birthplace tourist attraction in Warwickshire.
Brown paint was daubed on several windows and plaster work between Thursday evening and early on Friday, the Shakespeare Birthplace Trust said.
The trust, which looks after the Tudor house on Henley Street, Stratford-upon-Avon, said it had done a "good job" of cleaning it up, but marks remained.
Shakespeare's father owned the house at the time of his birth in 1564.
It was later inherited by Shakespeare and now attracts about 700,000 visitors each year, the trust added.
The charity said police were studying CCTV footage following the damage.
Chairman Professor Stanley Wells said: "It's most regrettable that anyone should feel an urge to deface an important historical landmark.
"I think it would be difficult to remove the marks entirely."