Just under the ribbon bar, where little notifications bars sometimes show useful information such as when a file is read-only or if a file needs to be Checked-Out to edit, a grey notification bar popped up an Information icon (blue circle with an 'i' in it) with the following text:

TAKE YOUR FILES WITH YOU View, share and edit files wherever you are with the OneDrive mobile app.

Followed by a button labelled "Download OneDrive".

This is on my work laptop, which has OneDrive installed and running.

I don't like this. Maybe I'm oversensitive because I also don't like OneDrive and I don't like advertising. Is this new? Slippery slopes aren't a valid point of argument, but this is yet another step, of many, down said slope.