I smile and say good morning or whatever, and get a range of replies from a pleasant reply to ignoring, but to me it is courteous behaviour when you are walking along a path somewhere. I now have some friends that I have known for years who I first met through just saying good morning. Also as I am a singer, quite often if I am out on my own I will be singing, anything from opera to portuguese fado to folk music and have usually had pleasant responses from people, many of whom have said - you sound very happy , or , it is good to hear someone singing etc. I get a range of responses from that to totally blanking me or turning off on another path. Doesnt bother me, they are entitled to be quiet if they wish and I dont intrude on someone who obviously does not want to make any contact with me