We saw the Ankh a couple of times in the latest episode of LOST. We saw that Paul had one and Amy kept it after his death, which later caused a fight between her and Horace. My next post will be about the other time we saw the Ankh (The Four Toed Statue). The rest of this post is a quote from another source that helps explains what the Ankh is.
The Ankh was, for the ancient Egyptians, the symbol (the actual Hieroglyphic sign) of life but it is an enduring icon that remains with us even today as a Christian cross. It is one of the most potent symbols represented in Egyptian art, often forming a part of decorative motifs.
The ankh seems at least to be an evolved form of, or associated with the Egyptian glyph for magical protection, sa. However, what the sign itself represents is often disputed. For example, Sir Alan Gardiner thought that it showed a sandal strap with the loop at the top forming the strap, but if so, the symbolism is obscure and so his theory has found little real favor early on. However, this interpretation seems to have received some acceptance among modern writers. It would seem that the ancient Egyptians called that part of the sandal 'nkh (exact pronunciation unknown). Because this word was composed of the same consonants as the word "life", the sign to represent that particular part of the sandal, was also used to write the word "life".
Source: The Ancient Ankh Symbol of Life