Why do tigers have small manes around their cheeks? Are they only found in males?

The longer hair around the cheeks is certainly more common in adult male tigers. I don't think there are any studies really testing if this has a function, but I would hypothesise that it related to testosterone expression. It could also have some signalling purpose (i.e. being attractive to females, or making the animal look more physically impressive to put off rival males) but I don't think this has ever been shown. Sadly, it would be quite hard to test this idea properly as there aren't enough tigers to make getting a decent sample size very easy.