Contact your estate attorney and file it as record along with anything else the attorney might need to protect the estate from anything he might do.
It also might be prudent to file for a general restraining order just in case he shows up out of the blue, sometimes people with those kinds of issues do those things.
I agree with all this especially about documentation of the note. I wonder if, as part of a restraining order request, police could ask the flower place for records of who sent it. That would be valuable proof down the road.