Ehwaz

In her Ancient Runes exam, Hermione gets Eihwaz and Ehwaz mixed up.

Eihwaz (or Yr) means "yew", like the wood used in Voldemort's wand, and it stands for defense and flexibility (like Snape's description of the dark arts). More on Eiwaz another time....

Ehwaz (or Eh) means "horse" and stands for movement, gradual growth, teamwork, and trust.

So, not only do we have horse-like creatures directly helping Harry (the centaur Firenze, the hippogriff Buckbeak/Witherwings, and the thestrals) and horse-like creatures that are generally good or helpful (the Abraxan winged horses from Beaubatons, the unicorns in the Forbidden Forest), but also Ron and Hermione. Wait...I know, they're humans, but Ehwaz is often portrayed as a pair of horses that work well as a team and help you acheive your goals. Ron and Hermione are a pair, and they help Harry. They could be viewed as Harry's Ehwaz. And...on McGonagall's chessboard, Ron was the mounted knight.

Ehwaz looks like an upper-case M. It's the same shape found in the body language of Hermione and Ron holding hands.... Ehwaz's polarity is male and female.

Another interpretation of this rune designates Harry as the Ehwaz, the leader of a team (of horses). This works just as well... maybe even better. Harry is working with a team of Ron and Hermione, two creative and highly individual people.

Ehwaz is the 19th rune in the futhark.

The 19th card of the major arcana of the tarot deck is the Sun... a definitely important symbol for Harry.