Gar does not have a letter equivalent.
There is no poem for Gar
Gar means spear. It is often thought to refer to Odhinn’s spear, which is also an epithet for Yggdrasil, the world tree from which Odhinn hung upon to gain the knowledge of the runes.
Many runesters have come across the “blank rune” in some contemporary sets and practices. From a historical practice, this is incorrect. Some groups and people who work with the extended Anglo-Saxon Futhorc utilize Gar as having similar meanings to that “blank rune”. In this case, it’s not the cosmic denial of information, but rather and indicator of potential, events and possibilities are still in the formative state and so anything is possible. So, don’t worry about things, and let them happen or act in the ways that you desire. I also see in it the sense of freedom of action. A time when previous actions are not creating the present, but rather you have the opportunity to plan anew and change the direction of things to come.