In most Asian cultures the Tiger holds very important meanings regarding strength and passion, which is why the symbol is heavily associated with Muay Thai boxing. As such, Tiger tattoos are extremely popular because the wearer associates the tigers traits to their own personality.
 
1) Tigers are known for their great strength. Their fast and wild nature represents them as a symbol of strength. Thus, people with fearless and bold personalities usually wear this tattoo.
2) The tiger's aggression and by association discipline are common themes. Where agression is vital to the mindset of a Muay Thai boxer, it is useless without great discipline and the ability to control it and unleash it when necessary. 
3) Tigers can also use their great strenght to defend themselves and protect those around them. Therefore, brave and stoic people with a protective attitude symbolise their nature by getting a tiger tattoo. On a side note, the Chinese often engrave a picture of the tiger on graveyards to offer protection to the dead.
4) Tigers are generally harmless unless they are provoked, and if someone comes in the way of a tiger, there is no way to escape. A tiger tattoo can also be worn as a warning to anyone who might provoke them.