Every jurisdiction will have their own version of this, but what you have done to the bus is criminal damage.
The elements of the offence (in Victoria, but every jurisdiction will have a corresponding offence with roughly the same elements) are:
- you damaged property,
- the property belonged to somebody else,
- you purposely damaged the property, or you knew or believed that damage would result from your actions, and
- you had no lawful excuse.
Lawful excuses include self-defence and duress. I don't get the impression that you thought that battering the bus was going to stop the bus driver trying to drive over you etc; you were just venting your anger. That's not a lawful excuse.
Maybe the police will exercise their discretion not to press charges, on the basis that you don't routinely go around battering mirrors and this was a one-off stressful situation, or that the damage is negligible. I don't know.
Note I am assuming you caused damage. I don't understand your photo; to me those mirrors looks like they're in the normal positions. If you just touched the mirror and maybe caused an inconvenience because the driver had to stop and re-adjust it, at best you're obstructing traffic (itself an offence but not as serious as criminal damage).
The law is pretty protective of property but it is generally not quite as protective of property as it is of persons. If you touch property without damaging it, generally nothing happens legally. If you touch a person without damaging them, you still commit assault.
References in Victoria:
I don't know your jurisdiction so I can't tell you whether your law has some statutory provision for interference with a bus to be a summary capital offence.
EDIT: There is also a summary offence called 'disorderly conduct', for which you can be fined (and for which you can be arrested, but not imprisoned). The definition in Victoria is 'Any person who behaves in a disorderly manner in a public place is guilty of an offence'. That's pretty broad and wouldn't require actual damage to anything.