Tip somebody the wink
Definition 1 of 1
Pro Tip 1/3Secretive Nature
Used when signaling covertly, especially to warn or inform about something private or undisclosed. 
During the exam, Lisa tipped Sam the wink about the invigilator approaching.
Pro Tip 2/3British Slang
Most common in the UK, it might confuse English speakers from other regions who aren't familiar with the idiom. 
When I lived in London, my mate always tipped me the wink about the best pubs.
Pro Tip 3/3Casual Use
The phrase is informal; it's best used among friends or in casual settings, not in formal communication. 
At the reunion, Jen tipped me the wink to avoid mentioning the prank we pulled back in the day.