When one's head is brought in contact with another - particularly when it's prolonged - it's a very strong affectionate body language signal. In the image above, a reunion between a daughter and survivor of the recent Korean Ferry sinking and her father is captured in such a moment.
An interesting nonverbal phenomenon is often displayed in the absence of another person however. Sargent Timothy D. Sayne was killed in action in Afghanistan on 18 September 2011. He was buried with at Arlington National Cemetery with full military honors. In the photo below, Thania, Sargent Sayne's wife is seen with her head against his gravestone. This action is not performed for physical support - rather for emotional connection, love - and especially affection. Here her husband's grave marker acts as a head surrogate. Despite being inanimate, such head-surrogate touching is also consistent with high sincerity quotients.
Nonverbal Communication Analysis # 1898: Heat, Hugs & Head Surrogates
Nonverbal Communication Analysis No. 2478: Acting Affectionate Engenders Affection Body Language and Strangers
Nonverbal Communication Analysis # 2317: "The Rescuing Hug" - Body Language of Human Touch & Kangaroo Care
Nonverbal Communication Analysis No. 2779: Rep. Vance McAllister Caught on Camera Kissing Staffer - Affection vs. Lust - What their Body Language says
Nonverbal Communication Analysis No. 2701: Cuddling, Romance, Affection and Foot-Shunning - Body Language Tells
Nonverbal Communication Analysis No. 2764: Embarrassment, Affection & Flirtation - Mila Kunis & Ashton Kutcher - Kiss Cam Body Language
Nonverbal Communication Analysis No. 2789: Gabriel García Márquez, Critical Evaluation and Body Language