Passing notes

As I left for work today, I obsessively checked my mailbox, and picked up a hand-scrawled note which read as follows:

HAPPY MEMORIAL DAY!
Love,
a neighbor

Which puzzled me immensely.
Why leave an anonymous note like this? If you don't know my name and vice-versa, you could at least give some indication who you are, like "your neighbors at number 73". But, why wish someone a happy memorial day? Although it has been apropriated as the unofficial start of summer, it's technically there to remember the fallen, hardly a cause for celebration. And, why drop me a note for memorial day, and not for Christmas, New Year, Easter or MLK day? My paranoid mind began wondering if this was some subtle dig, or the start of some kind of campaign. Was the note poisoned with some invisible contact poison? Perhaps it is just a child. Maybe I shouldn't worry, or bother making a blog post about this. But it's just odd enough to be disturbing.