The phrase "a friendly finger" is correct and usable in written English.
It can be used in contexts where you are describing a gesture or action that is gentle or supportive, often in a playful or light-hearted manner.
Example: "She gave him a friendly finger to encourage him to keep going, reminding him that he wasn't alone in this."
Alternatives: "a supportive gesture" or "a kind touch".
Come join the Cornell Orchards Store, Cornell Catering, and the Cornell Hard Cider Program Work Team for a family friendly Finger Lakes Cider Week event celebrating all things apples and cider!
Feb. 20, 2018, 7 03 p.m. Lindsey Vonn cast a quick glance toward the sky after finishing what was likely her final Olympic downhill run, shrugged her shoulders at seeing her time and shook a friendly index finger at her good friend.
The Peck Lab will lead orchard tours at 1 p.m. and 3 p.m. Come join the Cornell Orchards Store, Cornell Catering, and the Cornell Hard Cider Program Work Team for a family-friendly Finger Lakes Cider Week event celebrating all things apples and cider!
The resulting mac-and-cheeselets are both delicious and kid-friendly finger foods.
"I lost my left ring finger in a friendly fire training accident 10 years ago," one Facebook user wrote.
I recall that while I was kneeling down talking to her, she kept touching my nose with her little index finger in a friendly and playful manner; and asking me who I was, why was it that I wanted to know what had happened to her, what did I mean by this, and what was it that I was doing in her house.
In a slightly incongruous scene, a man with Millwall tattooed across his fingers is having a friendly chat with an officer wearing a fluorescent jacket with Football Liaison Officer written on the back.
I was going to give him the finger and he gave me the finger first," howls John Travolta, engaging Dustin Hoffman (who's two tables over) in a friendly biggest-stars-at-the-ball flip-off.
The dogs bark at one another in a friendly fashion, and then the lady with the terrier leans over and shakes her finger in the Scotty's face.
He had a finger amputated after he was bitten by a puff adder, and a "friendly" marsh mongoose chewed off half his lip.
