Oh how neat!!!! What kind?
This is a great white owl (aka, snowy owl, they usually aren't found below 60N latitude):
This is a juvenile great white owl:
This is a barn owl (at a glance it could look white):
As for it being an omen
I believe the universe sends you the message you're going to pick up on, so I don't necessarily see this as an omen. IOW, I'm forced to assume 75th is pretty skeptical of stuff like that so an owl landing on MY window sill would mean something quite differently from an owl landing on HIS window sill.
Actually it was Hedwig with a message from Harry Potter
This is a great white owl (aka, snowy owl, they usually aren't found below 60N latitude):

This is a juvenile great white owl:

This is a barn owl (at a glance it could look white):

As for it being an omen

Actually it was Hedwig with a message from Harry Potter
