I'm not sure if this is a joke, but I wouldn't be surprised if it's not. The city takes pet animals very seriously. It's a very progressive area and they spend lots of public money on all sorts of silly things. The fact that the 10 has apparently been doubled to 20 makes it seem like this isn't just a joke. There were two of these signs posted within 15 feet of each other.
Looks like the sign is real: https://www.theolympian.com/news/local/article216657700.html They're seriously offering $20,000 to catch a serial cat killer.
A final update: He didn't make it. While he could eat, drink and could get around amazingly well - the true escape artist - very powerful forward body strength - he could not control his bladder or bowels, constantly cried looking out a glass door to try to get outside, and the vet on closer examination of the x-rays said the top of the damaged vertebra was shattered for which he would remain in terrible pain and never regain bladder and bowel control nor additional use of his rear legs. He was miserable plus clearly had been made an outside cat by who had him the last years - as he continuously scratched at the glass to get out crying very loudly. While he was not aggressive towards us, he had no interest in us either - only trying anyway to get outside. After we both searched our hearts for the right thing to do, we authorized the vet to end the pain and suffer. It was not an easy decision but was wrong to just let him suffer trapped alone in a small room that he could never be safely released from in constant pain. Damn.