Number 54 is throwing a west side hand signal. It's origin is gang related. Specifically Bloods. However, it could just be a kid that picked up a signal and thinks it looks cool. I doubt there's any reason to worry.
Number 77 is throwing a sign that could mean many things. Hindu/Buddhists call it a Mudra. It's common to see statues of Buddha making this sign or one similar to it. It's supposed to facilitate calm thought. A more modern and western interpretation calls the sign the shocker and it's meaning is "two in the pink and one in the stink". Supposedly, some gangs use the sign with an alternative meaning, but it's not widespread.