A Sign and a Portent?

I've no idea where that phrase comes from, or why it popped into my head today.  I went for a short stroll on the path uphill from the house, and there was this knife stuck into the tag on the signpost.

Some helpful person trying to return lost property, or an expression of an opinion about the forthcoming referendum?

Google didn't help identify the source of the phrase, but it supplied the definition of  'portent' - 'an indication of something about to happen, especially something momentous.'

Pity it wasn't Andy M winning in Paris.