Although George R. R. Martin has been accused of criticizing the moral simplicity of Tolkien's work with his series A Song of Ice and Fire, he has often said that he read and enjoyed Lord of the Rings in his childhood and drew a lot of his inspiration for the series from Tolkien.
Now, I've only read the first four books in the series and it's been ages since I last read Lord of the Rings. However, are there any "tip-of-the-hat" or "subtle shout outs" to the Lord of the Rings stories or characters?
An example that I would think could be possible would be naming a city or character after a character or city from Lord of the Rings, etc. However, as the two books are in the same genre and share a lot of similar characteristics as it relates to setting, environment, etc. the possibilities for this would really seem to be endless.