@laurent - Yes, the item is still there (actually there are 4 pdfs in two notes)
Discourse directed me to this post
So on the Desktop I went to Tools>Note Attachments and ordered by size and the three large attachments were at the top of the list (even though I am sure I deleted the note - or at least the large PDF) so I deleted them.
But, after syncing desktop and android the banner is still there
EDIT: I should say 'was' there - I deleted a couple of other attachments that were less than 100 MB tho) and synced again and now the orange banner has gone
I am not sure if it went because I deleted more attachments or because it was just a matter of time.