Many people chronically confuse flirting behavior with affection - as well as sexual attraction/sexual behaviors with affection. While of course there is some overlap, these emotions and their corresponding body language signals are different phenomena. And there are of course many nonverbal displays of affection.
Last Christmas Tyne Owen proposed to his then-girlfriend Jamie in a very creative way (above video and captured in the image below). Head-to-head, head-to-shoulder and head-to-neck contact are all indicative of a high degree of affection. Head/neck tilting itself also has an emotional comfort and emotional vulnerability associated with it - e.g., the kind of vulnerability where you are "inviting" someone into your world - and not a vulnerability of weakness. Of course such affection and deliberate emotional exposure is not limited to romantic love.
Sincere affection displays are signals of true love and their waxing and maintenance are highly correlative with the crescendo and subsequent preservation of a healthy relationship ... while their waning indicates a rift, declination and, when precipitous, may even indicate infidelity. False affection displays are easily spotted if you know the nonverbal nuance.
Nonverbal Communication Analysis No. 3033: Reaction to Grand Jury's Decision regarding Eric Garner's Choke Hold Death
Nonverbal Communication Secret No. 1423: Head First Affection & Head Surrogate Hugs
Nonverbal Communication Analysis No. 2701: Cuddling, Romance, Affection and Foot-Shunning - Body Language Tells
Body Language Secret No. 105: Parental Affection and Love
Flirting and Romance Secret No. 39: Affectionate vs. Non-Affectionate Hug
Dating & Romance Secret No. 33: Who is the Dominant Partner?
Nonverbal Communication Analysis No. 2918: Lauren Bacall, Flirting and a "Come-hither look"