What will happen if a Horse on Earth suddenly got a cutie mark?

[HorsesandMOARGaloar 300]

By the time this was happening, the Horse is completely unaware of this.

 

Even if his Masters, a farmer and his family, noticed this weird phenomenon on its poor flanks.

 

What will its Masters say? Will the Equestrians abduct it and take it into their world? And what if some Brony of Pegasister suddenly chanced upon this poor creature?

[FabulousRarityFan18 12]

A horse with a cutie mark is similar to one of my scrapped story ideas. Rarity had a daughter who was forced to stay in the human world because Rarity unknowingly mated with a human. The human looked like a pony, but the DNA didn't change. Her daughter was an Anthropomorphic in Equestria, but she was able to appear full human in the human world. Several years later, Rarity decided to appear as a human horse to go to the human world. This is where I answer your question.

 

Rarity looks like a typical mare. She had a white coat with a brown mane. She didn't have her horn, but her cutie mark remained. Humans who saw this that that Rarity's owners drew the cutie mark on her and thought they were bronies. They paid no mind. Soon, when they noticed that the cutie mark was not drawn, but it was part of her, it got a lot of people surprised. Humans kidnapped her and forced her to be an object of display. 

 

Eventually, her daughter fell in love with her without knowing that was her mother. She was able to buy Rarity and took her home. Rarity wasn't excited about her daughter owning her, but she went along with her anyways. It was much better than the mistreatment of the other humans. Her daughter decided to ride her, and that was when her plan was taken into action. Rarity is not like a human pony, so when her daughter tried to control her, she wasn't able to. Rarity galloped as fast as she can without obeying any command from her daughter. She then stopped in a forest in front of a mirror and let her daughter off. 

 

Before Rarity nudged her daughter to go into the mirror, she wrote, "I found you" on the ground which surprised her daughter. Then it was scrapped from here. 

 

Your question is answered in the second paragraph. 

[Kel_Grym 1,917]

Unless they start talking, we'd still make glue out of em.

[I used to be a stranger 7,994]

It is not illegal to tatoo or brand a horse.

Tatooing is impractical however, because horses are covered with fine fur that would cover it up.

[Doctor Shuu 797]

"What an odd birthmark."

[Radiance64 7,053]

Magic is coming.

[baba_booey 4,303]

My reaction would simply be..

 

[aidanbrony 12]

ALL HAIL THE CUTIE MARK