If you drive in the UK, you'll see road signs that have one word on them - STOP - and this is perfectly acceptable. English learners are sometimes taught as a "rule" that a simple sentence must have a subject and a verb as a minimum, but that isn't the case with orders.

Orders, such as on signs and slogans, don't have to follow the grammatical structure of everyday speech. They are often in the *imperative mood*, aimed at the reader (or hearer) who is the implied subject. In effect it is asking *you* to obey the order.

"Stop Asian Hate" is punchy and succinct - it seems clear to me that it is a campaign to stop hate *against* Asian people - what else could it mean? The only other alternative would be that it is a campaign to stop Asian people hating something else - but what? It wouldn't be a very good slogan if there was no object.