[@PlatinumSkink] you know it's a familiar because of its magic patterns.

As seen when Kyoko goes to fight Octavia, she says it has a similar magic pattern to the Witch at the train station, and she could tell by using her soul gem.

We can assume then, that all Witches and Familiars (being split parts of a Witch) all have a certain magical patterns as well.

Given this, and that Familiars are weaker than Witches, we can guess that the magical pattern will be weaker as well.