In communication as the recipient your job is to try to understand what is meant, not what is said.
Conversely, as the communicator, your job is to say what you mean, and ensure what is said is in line with what is meant. The added complexity is that to do this you need to have a decent grasp on what recipients will hear (as in "understand intent," as opposed to the literal words that they physically hear)
Or, actually listen to people. Your call.
The slogan makes many people think you're advocating an unreasonable idea that you're not actually advocating. Do you think that makes for a good slogan?
Edit: I apologize. I missed where you said it's a bad slogan, and took your defense of it as implying it's good.
The same ones you use to understand what the word "police" means. Human language isn't a direct, thought transmission mechanism (especially with short utterances). Ambiguity and uncertainty and reliance on shared context are inherent. The artificial language Toki Pona gives an exaggerated demonstration of this [1].
> The slogan makes many people think you're advocating an unreasonable idea that you're not actually advocating. Do you think that makes for a good slogan?
No one can ever cram the nuance of a complex political position onto a slogan to fit on a sign. Inevitably someone will misunderstand to some degree, then have to go on to read one of the hundreds of articles titled "what does 'defund the police' mean?" to correct your misunderstanding.
If you're searching for some optimal slogan, you're not going to find it. Sure there are alternatives, but a couple things count in "defund the police"'s favor: 1) it succinctly indicates the topic and 2) pretty clearly conveys the opinion that a radical break with prior reform efforts is needed. "Abolish the police" does the same, except it's more amplified.