I think its sweet and cute and cute and everything that everyone else has said.
Sometimes it can be annoying like the other day, me and my bf had a stupid disagreement jus before i had to go home. We sort of made up, thre were no bad feelings or anything but as i left his house he kissed my forehead and shut the door. Normally he does kiss my lips and cuddles me, walks me home. Very affectionate and never wants me to leave, then a kiss on the forehead.
But ususlly, a kiss on the forehead is lovely. Especially when you are in one of those hugs where you dont want to let go, they last forever and then (as hes taller) he bends down a bit and kisses my forehead. Then its sweet.
Anyway, why are you asking?