The animal-loving star climbed onto scaffolding supporting the sign in San Diego, California in May (14) and pasted the word "sucks" next to the mileage indicator for the aquatic themepark, where killer whales and other marine creatures perform for the public.
The 40 year old, real name Stephen Glover, went public with his act of vandalism when he posted a YouTube video of himself climbing the freeway sign in August (14) and California Highway Patrol officials immediately recommended he be charged with vandalism and trespassing.
On Monday (01Dec14), he was issued a traffic citation, and told he has 20 days to settle a $239 (£159) fine.
Lawmakers insisted the stunt posed a distraction for drivers and therefore could have caused an accident.
Steve-O, who is currently on vacation in Morocco, was not in court for the ruling.
People for the Ethical Treatment of Animals bosses have already agreed to pay any fine assessed against Steve-O.
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