The Ankh for the Egyptians was a symbol for life and is the most recognised symbol of Ancient Egypt. It is argued that the ankh is associated with the Egyptian glyph of magical protection (sa) but there are many theories that are being thrown about such as the loop symbolising the rising of the sun, or another one is the loop is a cartouche  which would have the pharoahs name in it.

The ankh has been depicted in tombs often as a symbol which passes life onto someone else or helps them pass to the netherworld. Either way you want to go in terms of symbolisim the ankh tattoo will provide long life for whomever has it.