what do all those hand signs mean?

I'm always seeing Japanese girls posing with all sorts of hand signs. Some I recognize, like peace signs. Others I can figure out, like the curled fist looking like a cat's paw. But there are a lot, frankly, that mystify me. Anybody know a good source for detailing what all those hand signs mean? Like when a girl makes the letter C or holds her fingers in a partially curled peace sign at the sides of her head (ears?).

It's mainly just to look cute, there's no deep reason for them.
it's just "this is a heart, so cute" or "this is what a cute animal does, uwu" stuff like that.

or it's all a secret code and you're the first to notice.
( Í¡° ͜ʖ Í¡°)

Mostly to look cute, sometimes they are throwing heart signs or they could even be gang signs

The gang signs comment made me spit soda.

Yes, all Japanese girls are secretly part of a gang. Obviously they stand for the following:

• 
  > Peace Sign: Yo, we good
  > Double Peace Sign: Yo, we real good
  > Curled Peace Sign (Bunny Ears): Yo, feeling cute today
  > Cat Paw: Yo, I love cats and/or am feeling a bit adventurous today
  > Heart Sign: Yo, I want to look cute, but am not actually feeling cute
  

Posers, the lot of them.

she is greeting you. peace sign her back.

I think one hand sign that's meaning isn't obvious is the sideways "okay" sign, which means "money." Kind of similar to how in the US someone might rub their thumb and index + middle fingers together to indicate money.